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[PATCH v12 6/7] Row pattern recognition patch (tests). 340+ messages / 2 participants [nested] [flat]
* [PATCH v12 6/7] Row pattern recognition patch (tests). @ 2023-12-04 11:23 Tatsuo Ishii <ishii@postgresql.org> 0 siblings, 0 replies; 340+ messages in thread From: Tatsuo Ishii @ 2023-12-04 11:23 UTC (permalink / raw) --- src/test/regress/expected/rpr.out | 821 +++++++++++++++++++++++++++++ src/test/regress/parallel_schedule | 2 +- src/test/regress/sql/rpr.sql | 392 ++++++++++++++ 3 files changed, 1214 insertions(+), 1 deletion(-) create mode 100644 src/test/regress/expected/rpr.out create mode 100644 src/test/regress/sql/rpr.sql diff --git a/src/test/regress/expected/rpr.out b/src/test/regress/expected/rpr.out new file mode 100644 index 0000000000..e8998ebf45 --- /dev/null +++ b/src/test/regress/expected/rpr.out @@ -0,0 +1,821 @@ +-- +-- Test for row pattern definition clause +-- +CREATE TEMP TABLE stock ( + company TEXT, + tdate DATE, + price INTEGER +); +INSERT INTO stock VALUES ('company1', '2023-07-01', 100); +INSERT INTO stock VALUES ('company1', '2023-07-02', 200); +INSERT INTO stock VALUES ('company1', '2023-07-03', 150); +INSERT INTO stock VALUES ('company1', '2023-07-04', 140); +INSERT INTO stock VALUES ('company1', '2023-07-05', 150); +INSERT INTO stock VALUES ('company1', '2023-07-06', 90); +INSERT INTO stock VALUES ('company1', '2023-07-07', 110); +INSERT INTO stock VALUES ('company1', '2023-07-08', 130); +INSERT INTO stock VALUES ('company1', '2023-07-09', 120); +INSERT INTO stock VALUES ('company1', '2023-07-10', 130); +INSERT INTO stock VALUES ('company2', '2023-07-01', 50); +INSERT INTO stock VALUES ('company2', '2023-07-02', 2000); +INSERT INTO stock VALUES ('company2', '2023-07-03', 1500); +INSERT INTO stock VALUES ('company2', '2023-07-04', 1400); +INSERT INTO stock VALUES ('company2', '2023-07-05', 1500); +INSERT INTO stock VALUES ('company2', '2023-07-06', 60); +INSERT INTO stock VALUES ('company2', '2023-07-07', 1100); +INSERT INTO stock VALUES ('company2', '2023-07-08', 1300); +INSERT INTO stock VALUES ('company2', '2023-07-09', 1200); +INSERT INTO stock VALUES ('company2', '2023-07-10', 1300); +SELECT * FROM stock; + company | tdate | price +----------+------------+------- + company1 | 07-01-2023 | 100 + company1 | 07-02-2023 | 200 + company1 | 07-03-2023 | 150 + company1 | 07-04-2023 | 140 + company1 | 07-05-2023 | 150 + company1 | 07-06-2023 | 90 + company1 | 07-07-2023 | 110 + company1 | 07-08-2023 | 130 + company1 | 07-09-2023 | 120 + company1 | 07-10-2023 | 130 + company2 | 07-01-2023 | 50 + company2 | 07-02-2023 | 2000 + company2 | 07-03-2023 | 1500 + company2 | 07-04-2023 | 1400 + company2 | 07-05-2023 | 1500 + company2 | 07-06-2023 | 60 + company2 | 07-07-2023 | 1100 + company2 | 07-08-2023 | 1300 + company2 | 07-09-2023 | 1200 + company2 | 07-10-2023 | 1300 +(20 rows) + +-- basic test using PREV +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | nth_second +----------+------------+-------+-------------+------------+------------ + company1 | 07-01-2023 | 100 | 100 | 140 | 07-02-2023 + company1 | 07-02-2023 | 200 | | | + company1 | 07-03-2023 | 150 | | | + company1 | 07-04-2023 | 140 | | | + company1 | 07-05-2023 | 150 | | | + company1 | 07-06-2023 | 90 | 90 | 120 | 07-07-2023 + company1 | 07-07-2023 | 110 | | | + company1 | 07-08-2023 | 130 | | | + company1 | 07-09-2023 | 120 | | | + company1 | 07-10-2023 | 130 | | | + company2 | 07-01-2023 | 50 | 50 | 1400 | 07-02-2023 + company2 | 07-02-2023 | 2000 | | | + company2 | 07-03-2023 | 1500 | | | + company2 | 07-04-2023 | 1400 | | | + company2 | 07-05-2023 | 1500 | | | + company2 | 07-06-2023 | 60 | 60 | 1200 | 07-07-2023 + company2 | 07-07-2023 | 1100 | | | + company2 | 07-08-2023 | 1300 | | | + company2 | 07-09-2023 | 1200 | | | + company2 | 07-10-2023 | 1300 | | | +(20 rows) + +-- basic test using PREV. UP appears twice +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+ UP+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | nth_second +----------+------------+-------+-------------+------------+------------ + company1 | 07-01-2023 | 100 | 100 | 150 | 07-02-2023 + company1 | 07-02-2023 | 200 | | | + company1 | 07-03-2023 | 150 | | | + company1 | 07-04-2023 | 140 | | | + company1 | 07-05-2023 | 150 | | | + company1 | 07-06-2023 | 90 | 90 | 130 | 07-07-2023 + company1 | 07-07-2023 | 110 | | | + company1 | 07-08-2023 | 130 | | | + company1 | 07-09-2023 | 120 | | | + company1 | 07-10-2023 | 130 | | | + company2 | 07-01-2023 | 50 | 50 | 1500 | 07-02-2023 + company2 | 07-02-2023 | 2000 | | | + company2 | 07-03-2023 | 1500 | | | + company2 | 07-04-2023 | 1400 | | | + company2 | 07-05-2023 | 1500 | | | + company2 | 07-06-2023 | 60 | 60 | 1300 | 07-07-2023 + company2 | 07-07-2023 | 1100 | | | + company2 | 07-08-2023 | 1300 | | | + company2 | 07-09-2023 | 1200 | | | + company2 | 07-10-2023 | 1300 | | | +(20 rows) + +-- basic test using PREV. Use '*' +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP* DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | nth_second +----------+------------+-------+-------------+------------+------------ + company1 | 07-01-2023 | 100 | 100 | 140 | 07-02-2023 + company1 | 07-02-2023 | 200 | | | + company1 | 07-03-2023 | 150 | | | + company1 | 07-04-2023 | 140 | | | + company1 | 07-05-2023 | 150 | 150 | 90 | 07-06-2023 + company1 | 07-06-2023 | 90 | | | + company1 | 07-07-2023 | 110 | 110 | 120 | 07-08-2023 + company1 | 07-08-2023 | 130 | | | + company1 | 07-09-2023 | 120 | | | + company1 | 07-10-2023 | 130 | | | + company2 | 07-01-2023 | 50 | 50 | 1400 | 07-02-2023 + company2 | 07-02-2023 | 2000 | | | + company2 | 07-03-2023 | 1500 | | | + company2 | 07-04-2023 | 1400 | | | + company2 | 07-05-2023 | 1500 | 1500 | 60 | 07-06-2023 + company2 | 07-06-2023 | 60 | | | + company2 | 07-07-2023 | 1100 | 1100 | 1200 | 07-08-2023 + company2 | 07-08-2023 | 1300 | | | + company2 | 07-09-2023 | 1200 | | | + company2 | 07-10-2023 | 1300 | | | +(20 rows) + +-- basic test with none greedy pattern +SELECT company, tdate, price, count(*) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (A A A) + DEFINE + A AS price >= 140 AND price <= 150 +); + company | tdate | price | count +----------+------------+-------+------- + company1 | 07-01-2023 | 100 | 0 + company1 | 07-02-2023 | 200 | 0 + company1 | 07-03-2023 | 150 | 3 + company1 | 07-04-2023 | 140 | + company1 | 07-05-2023 | 150 | + company1 | 07-06-2023 | 90 | 0 + company1 | 07-07-2023 | 110 | 0 + company1 | 07-08-2023 | 130 | 0 + company1 | 07-09-2023 | 120 | 0 + company1 | 07-10-2023 | 130 | 0 + company2 | 07-01-2023 | 50 | 0 + company2 | 07-02-2023 | 2000 | 0 + company2 | 07-03-2023 | 1500 | 0 + company2 | 07-04-2023 | 1400 | 0 + company2 | 07-05-2023 | 1500 | 0 + company2 | 07-06-2023 | 60 | 0 + company2 | 07-07-2023 | 1100 | 0 + company2 | 07-08-2023 | 1300 | 0 + company2 | 07-09-2023 | 1200 | 0 + company2 | 07-10-2023 | 1300 | 0 +(20 rows) + +-- last_value() should remain consistent +SELECT company, tdate, price, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | last_value +----------+------------+-------+------------ + company1 | 07-01-2023 | 100 | 140 + company1 | 07-02-2023 | 200 | + company1 | 07-03-2023 | 150 | + company1 | 07-04-2023 | 140 | + company1 | 07-05-2023 | 150 | + company1 | 07-06-2023 | 90 | 120 + company1 | 07-07-2023 | 110 | + company1 | 07-08-2023 | 130 | + company1 | 07-09-2023 | 120 | + company1 | 07-10-2023 | 130 | + company2 | 07-01-2023 | 50 | 1400 + company2 | 07-02-2023 | 2000 | + company2 | 07-03-2023 | 1500 | + company2 | 07-04-2023 | 1400 | + company2 | 07-05-2023 | 1500 | + company2 | 07-06-2023 | 60 | 1200 + company2 | 07-07-2023 | 1100 | + company2 | 07-08-2023 | 1300 | + company2 | 07-09-2023 | 1200 | + company2 | 07-10-2023 | 1300 | +(20 rows) + +-- omit "START" in DEFINE but it is ok because "START AS TRUE" is +-- implicitly defined. per spec. +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | nth_second +----------+------------+-------+-------------+------------+------------ + company1 | 07-01-2023 | 100 | 100 | 140 | 07-02-2023 + company1 | 07-02-2023 | 200 | | | + company1 | 07-03-2023 | 150 | | | + company1 | 07-04-2023 | 140 | | | + company1 | 07-05-2023 | 150 | | | + company1 | 07-06-2023 | 90 | 90 | 120 | 07-07-2023 + company1 | 07-07-2023 | 110 | | | + company1 | 07-08-2023 | 130 | | | + company1 | 07-09-2023 | 120 | | | + company1 | 07-10-2023 | 130 | | | + company2 | 07-01-2023 | 50 | 50 | 1400 | 07-02-2023 + company2 | 07-02-2023 | 2000 | | | + company2 | 07-03-2023 | 1500 | | | + company2 | 07-04-2023 | 1400 | | | + company2 | 07-05-2023 | 1500 | | | + company2 | 07-06-2023 | 60 | 60 | 1200 | 07-07-2023 + company2 | 07-07-2023 | 1100 | | | + company2 | 07-08-2023 | 1300 | | | + company2 | 07-09-2023 | 1200 | | | + company2 | 07-10-2023 | 1300 | | | +(20 rows) + +-- the first row start with less than or equal to 100 +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (LOWPRICE UP+ DOWN+) + DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | 100 | 140 + company1 | 07-02-2023 | 200 | | + company1 | 07-03-2023 | 150 | | + company1 | 07-04-2023 | 140 | | + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | 90 | 120 + company1 | 07-07-2023 | 110 | | + company1 | 07-08-2023 | 130 | | + company1 | 07-09-2023 | 120 | | + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | 50 | 1400 + company2 | 07-02-2023 | 2000 | | + company2 | 07-03-2023 | 1500 | | + company2 | 07-04-2023 | 1400 | | + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | 60 | 1200 + company2 | 07-07-2023 | 1100 | | + company2 | 07-08-2023 | 1300 | | + company2 | 07-09-2023 | 1200 | | + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- second row raises 120% +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (LOWPRICE UP+ DOWN+) + DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price) * 1.2, + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | 100 | 140 + company1 | 07-02-2023 | 200 | | + company1 | 07-03-2023 | 150 | | + company1 | 07-04-2023 | 140 | | + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | | + company1 | 07-07-2023 | 110 | | + company1 | 07-08-2023 | 130 | | + company1 | 07-09-2023 | 120 | | + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | 50 | 1400 + company2 | 07-02-2023 | 2000 | | + company2 | 07-03-2023 | 1500 | | + company2 | 07-04-2023 | 1400 | | + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | | + company2 | 07-07-2023 | 1100 | | + company2 | 07-08-2023 | 1300 | | + company2 | 07-09-2023 | 1200 | | + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- using NEXT +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UPDOWN) + DEFINE + START AS TRUE, + UPDOWN AS price > PREV(price) AND price > NEXT(price) +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | 100 | 200 + company1 | 07-02-2023 | 200 | | + company1 | 07-03-2023 | 150 | | + company1 | 07-04-2023 | 140 | 140 | 150 + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | | + company1 | 07-07-2023 | 110 | 110 | 130 + company1 | 07-08-2023 | 130 | | + company1 | 07-09-2023 | 120 | | + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | 50 | 2000 + company2 | 07-02-2023 | 2000 | | + company2 | 07-03-2023 | 1500 | | + company2 | 07-04-2023 | 1400 | 1400 | 1500 + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | | + company2 | 07-07-2023 | 1100 | 1100 | 1300 + company2 | 07-08-2023 | 1300 | | + company2 | 07-09-2023 | 1200 | | + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- using AFTER MATCH SKIP TO NEXT ROW +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP TO NEXT ROW + INITIAL + PATTERN (START UPDOWN) + DEFINE + START AS TRUE, + UPDOWN AS price > PREV(price) AND price > NEXT(price) +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | 100 | 200 + company1 | 07-02-2023 | 200 | | + company1 | 07-03-2023 | 150 | | + company1 | 07-04-2023 | 140 | 140 | 150 + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | | + company1 | 07-07-2023 | 110 | 110 | 130 + company1 | 07-08-2023 | 130 | | + company1 | 07-09-2023 | 120 | | + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | 50 | 2000 + company2 | 07-02-2023 | 2000 | | + company2 | 07-03-2023 | 1500 | | + company2 | 07-04-2023 | 1400 | 1400 | 1500 + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | | + company2 | 07-07-2023 | 1100 | 1100 | 1300 + company2 | 07-08-2023 | 1300 | | + company2 | 07-09-2023 | 1200 | | + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- match everything +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + INITIAL + PATTERN (A+) + DEFINE + A AS TRUE +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | 100 | 130 + company1 | 07-02-2023 | 200 | | + company1 | 07-03-2023 | 150 | | + company1 | 07-04-2023 | 140 | | + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | | + company1 | 07-07-2023 | 110 | | + company1 | 07-08-2023 | 130 | | + company1 | 07-09-2023 | 120 | | + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | 50 | 1300 + company2 | 07-02-2023 | 2000 | | + company2 | 07-03-2023 | 1500 | | + company2 | 07-04-2023 | 1400 | | + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | | + company2 | 07-07-2023 | 1100 | | + company2 | 07-08-2023 | 1300 | | + company2 | 07-09-2023 | 1200 | | + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- backtracking with reclassification of rows +-- using AFTER MATCH SKIP PAST LAST ROW +SELECT company, tdate, price, first_value(tdate) OVER w, last_value(tdate) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + INITIAL + PATTERN (A+ B+) + DEFINE + A AS price > 100, + B AS price > 100 +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | | + company1 | 07-02-2023 | 200 | 07-02-2023 | 07-05-2023 + company1 | 07-03-2023 | 150 | | + company1 | 07-04-2023 | 140 | | + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | | + company1 | 07-07-2023 | 110 | 07-07-2023 | 07-10-2023 + company1 | 07-08-2023 | 130 | | + company1 | 07-09-2023 | 120 | | + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | | + company2 | 07-02-2023 | 2000 | 07-02-2023 | 07-05-2023 + company2 | 07-03-2023 | 1500 | | + company2 | 07-04-2023 | 1400 | | + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | | + company2 | 07-07-2023 | 1100 | 07-07-2023 | 07-10-2023 + company2 | 07-08-2023 | 1300 | | + company2 | 07-09-2023 | 1200 | | + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- backtracking with reclassification of rows +-- using AFTER MATCH SKIP TO NEXT ROW +SELECT company, tdate, price, first_value(tdate) OVER w, last_value(tdate) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP TO NEXT ROW + INITIAL + PATTERN (A+ B+) + DEFINE + A AS price > 100, + B AS price > 100 +); + company | tdate | price | first_value | last_value +----------+------------+-------+-------------+------------ + company1 | 07-01-2023 | 100 | | + company1 | 07-02-2023 | 200 | 07-02-2023 | 07-05-2023 + company1 | 07-03-2023 | 150 | 07-03-2023 | 07-05-2023 + company1 | 07-04-2023 | 140 | 07-04-2023 | 07-05-2023 + company1 | 07-05-2023 | 150 | | + company1 | 07-06-2023 | 90 | | + company1 | 07-07-2023 | 110 | 07-07-2023 | 07-10-2023 + company1 | 07-08-2023 | 130 | 07-08-2023 | 07-10-2023 + company1 | 07-09-2023 | 120 | 07-09-2023 | 07-10-2023 + company1 | 07-10-2023 | 130 | | + company2 | 07-01-2023 | 50 | | + company2 | 07-02-2023 | 2000 | 07-02-2023 | 07-05-2023 + company2 | 07-03-2023 | 1500 | 07-03-2023 | 07-05-2023 + company2 | 07-04-2023 | 1400 | 07-04-2023 | 07-05-2023 + company2 | 07-05-2023 | 1500 | | + company2 | 07-06-2023 | 60 | | + company2 | 07-07-2023 | 1100 | 07-07-2023 | 07-10-2023 + company2 | 07-08-2023 | 1300 | 07-08-2023 | 07-10-2023 + company2 | 07-09-2023 | 1200 | 07-09-2023 | 07-10-2023 + company2 | 07-10-2023 | 1300 | | +(20 rows) + +-- ROWS BETWEEN CURRENT ROW AND offset FOLLOWING +SELECT company, tdate, price, first_value(tdate) OVER w, last_value(tdate) OVER w, + count(*) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | count +----------+------------+-------+-------------+------------+------- + company1 | 07-01-2023 | 100 | 07-01-2023 | 07-03-2023 | 3 + company1 | 07-02-2023 | 200 | | | + company1 | 07-03-2023 | 150 | | | + company1 | 07-04-2023 | 140 | 07-04-2023 | 07-06-2023 | 3 + company1 | 07-05-2023 | 150 | | | + company1 | 07-06-2023 | 90 | | | + company1 | 07-07-2023 | 110 | 07-07-2023 | 07-09-2023 | 3 + company1 | 07-08-2023 | 130 | | | + company1 | 07-09-2023 | 120 | | | + company1 | 07-10-2023 | 130 | | | 0 + company2 | 07-01-2023 | 50 | 07-01-2023 | 07-03-2023 | 3 + company2 | 07-02-2023 | 2000 | | | + company2 | 07-03-2023 | 1500 | | | + company2 | 07-04-2023 | 1400 | 07-04-2023 | 07-06-2023 | 3 + company2 | 07-05-2023 | 1500 | | | + company2 | 07-06-2023 | 60 | | | + company2 | 07-07-2023 | 1100 | 07-07-2023 | 07-09-2023 | 3 + company2 | 07-08-2023 | 1300 | | | + company2 | 07-09-2023 | 1200 | | | + company2 | 07-10-2023 | 1300 | | | 0 +(20 rows) + +-- +-- Aggregates +-- +-- using AFTER MATCH SKIP PAST LAST ROW +SELECT company, tdate, price, + first_value(price) OVER w, + last_value(price) OVER w, + max(price) OVER w, + min(price) OVER w, + sum(price) OVER w, + avg(price) OVER w, + count(price) OVER w +FROM stock +WINDOW w AS ( +PARTITION BY company +ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING +AFTER MATCH SKIP PAST LAST ROW +INITIAL +PATTERN (START UP+ DOWN+) +DEFINE +START AS TRUE, +UP AS price > PREV(price), +DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | max | min | sum | avg | count +----------+------------+-------+-------------+------------+------+-----+------+-----------------------+------- + company1 | 07-01-2023 | 100 | 100 | 140 | 200 | 100 | 590 | 147.5000000000000000 | 4 + company1 | 07-02-2023 | 200 | | | | | | | + company1 | 07-03-2023 | 150 | | | | | | | + company1 | 07-04-2023 | 140 | | | | | | | + company1 | 07-05-2023 | 150 | | | | | | | 0 + company1 | 07-06-2023 | 90 | 90 | 120 | 130 | 90 | 450 | 112.5000000000000000 | 4 + company1 | 07-07-2023 | 110 | | | | | | | + company1 | 07-08-2023 | 130 | | | | | | | + company1 | 07-09-2023 | 120 | | | | | | | + company1 | 07-10-2023 | 130 | | | | | | | 0 + company2 | 07-01-2023 | 50 | 50 | 1400 | 2000 | 50 | 4950 | 1237.5000000000000000 | 4 + company2 | 07-02-2023 | 2000 | | | | | | | + company2 | 07-03-2023 | 1500 | | | | | | | + company2 | 07-04-2023 | 1400 | | | | | | | + company2 | 07-05-2023 | 1500 | | | | | | | 0 + company2 | 07-06-2023 | 60 | 60 | 1200 | 1300 | 60 | 3660 | 915.0000000000000000 | 4 + company2 | 07-07-2023 | 1100 | | | | | | | + company2 | 07-08-2023 | 1300 | | | | | | | + company2 | 07-09-2023 | 1200 | | | | | | | + company2 | 07-10-2023 | 1300 | | | | | | | 0 +(20 rows) + +-- using AFTER MATCH SKIP TO NEXT ROW +SELECT company, tdate, price, + first_value(price) OVER w, + last_value(price) OVER w, + max(price) OVER w, + min(price) OVER w, + sum(price) OVER w, + avg(price) OVER w, + count(price) OVER w +FROM stock +WINDOW w AS ( +PARTITION BY company +ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING +AFTER MATCH SKIP TO NEXT ROW +INITIAL +PATTERN (START UP+ DOWN+) +DEFINE +START AS TRUE, +UP AS price > PREV(price), +DOWN AS price < PREV(price) +); + company | tdate | price | first_value | last_value | max | min | sum | avg | count +----------+------------+-------+-------------+------------+------+------+------+-----------------------+------- + company1 | 07-01-2023 | 100 | 100 | 140 | 200 | 100 | 590 | 147.5000000000000000 | 4 + company1 | 07-02-2023 | 200 | | | | | | | 0 + company1 | 07-03-2023 | 150 | | | | | | | 0 + company1 | 07-04-2023 | 140 | 140 | 90 | 150 | 90 | 380 | 126.6666666666666667 | 3 + company1 | 07-05-2023 | 150 | | | | | | | 0 + company1 | 07-06-2023 | 90 | 90 | 120 | 130 | 90 | 450 | 112.5000000000000000 | 4 + company1 | 07-07-2023 | 110 | 110 | 120 | 130 | 110 | 360 | 120.0000000000000000 | 3 + company1 | 07-08-2023 | 130 | | | | | | | 0 + company1 | 07-09-2023 | 120 | | | | | | | 0 + company1 | 07-10-2023 | 130 | | | | | | | 0 + company2 | 07-01-2023 | 50 | 50 | 1400 | 2000 | 50 | 4950 | 1237.5000000000000000 | 4 + company2 | 07-02-2023 | 2000 | | | | | | | 0 + company2 | 07-03-2023 | 1500 | | | | | | | 0 + company2 | 07-04-2023 | 1400 | 1400 | 60 | 1500 | 60 | 2960 | 986.6666666666666667 | 3 + company2 | 07-05-2023 | 1500 | | | | | | | 0 + company2 | 07-06-2023 | 60 | 60 | 1200 | 1300 | 60 | 3660 | 915.0000000000000000 | 4 + company2 | 07-07-2023 | 1100 | 1100 | 1200 | 1300 | 1100 | 3600 | 1200.0000000000000000 | 3 + company2 | 07-08-2023 | 1300 | | | | | | | 0 + company2 | 07-09-2023 | 1200 | | | | | | | 0 + company2 | 07-10-2023 | 1300 | | | | | | | 0 +(20 rows) + +-- JOIN case +CREATE TEMP TABLE t1 (i int, v1 int); +CREATE TEMP TABLE t2 (j int, v2 int); +INSERT INTO t1 VALUES(1,10); +INSERT INTO t1 VALUES(1,11); +INSERT INTO t1 VALUES(1,12); +INSERT INTO t2 VALUES(2,10); +INSERT INTO t2 VALUES(2,11); +INSERT INTO t2 VALUES(2,12); +SELECT * FROM t1, t2 WHERE t1.v1 <= 11 AND t2.v2 <= 11; + i | v1 | j | v2 +---+----+---+---- + 1 | 10 | 2 | 10 + 1 | 10 | 2 | 11 + 1 | 11 | 2 | 10 + 1 | 11 | 2 | 11 +(4 rows) + +SELECT *, count(*) OVER w FROM t1, t2 +WINDOW w AS ( + PARTITION BY t1.i + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (A) + DEFINE + A AS v1 <= 11 AND v2 <= 11 +); + i | v1 | j | v2 | count +---+----+---+----+------- + 1 | 10 | 2 | 10 | 1 + 1 | 10 | 2 | 11 | 1 + 1 | 10 | 2 | 12 | 0 + 1 | 11 | 2 | 10 | 1 + 1 | 11 | 2 | 11 | 1 + 1 | 11 | 2 | 12 | 0 + 1 | 12 | 2 | 10 | 0 + 1 | 12 | 2 | 11 | 0 + 1 | 12 | 2 | 12 | 0 +(9 rows) + +-- WITH case +WITH wstock AS ( + SELECT * FROM stock WHERE tdate < '2023-07-08' +) +SELECT tdate, price, +first_value(tdate) OVER w, +count(*) OVER w + FROM wstock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + tdate | price | first_value | count +------------+-------+-------------+------- + 07-01-2023 | 100 | 07-01-2023 | 4 + 07-02-2023 | 200 | | + 07-03-2023 | 150 | | + 07-04-2023 | 140 | | + 07-05-2023 | 150 | | 0 + 07-06-2023 | 90 | | 0 + 07-07-2023 | 110 | | 0 + 07-01-2023 | 50 | 07-01-2023 | 4 + 07-02-2023 | 2000 | | + 07-03-2023 | 1500 | | + 07-04-2023 | 1400 | | + 07-05-2023 | 1500 | | 0 + 07-06-2023 | 60 | | 0 + 07-07-2023 | 1100 | | 0 +(14 rows) + +-- +-- Error cases +-- +-- row pattern definition variable name must not appear more than once +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + ORDER BY tdate + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price), + UP AS price > PREV(price) +); +ERROR: syntax error at or near "ORDER" +LINE 6: ORDER BY tdate + ^ +-- pattern variable name must appear in DEFINE +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+ END) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); +ERROR: syntax error at or near "END" +LINE 8: PATTERN (START UP+ DOWN+ END) + ^ +-- FRAME must start at current row when row patttern recognition is used +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); +ERROR: FRAME must start at current row when row patttern recognition is used +-- SEEK is not supported +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP TO NEXT ROW + SEEK + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); +ERROR: SEEK is not supported +LINE 8: SEEK + ^ +HINT: Use INITIAL. diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule index f0987ff537..a6542f3dea 100644 --- a/src/test/regress/parallel_schedule +++ b/src/test/regress/parallel_schedule @@ -98,7 +98,7 @@ test: publication subscription # Another group of parallel tests # select_views depends on create_view # ---------- -test: select_views portals_p2 foreign_key cluster dependency guc bitmapops combocid tsearch tsdicts foreign_data window xmlmap functional_deps advisory_lock indirect_toast equivclass +test: select_views portals_p2 foreign_key cluster dependency guc bitmapops combocid tsearch tsdicts foreign_data window xmlmap functional_deps advisory_lock indirect_toast equivclass rpr # ---------- # Another group of parallel tests (JSON related) diff --git a/src/test/regress/sql/rpr.sql b/src/test/regress/sql/rpr.sql new file mode 100644 index 0000000000..0a69cc0e11 --- /dev/null +++ b/src/test/regress/sql/rpr.sql @@ -0,0 +1,392 @@ +-- +-- Test for row pattern definition clause +-- + +CREATE TEMP TABLE stock ( + company TEXT, + tdate DATE, + price INTEGER +); +INSERT INTO stock VALUES ('company1', '2023-07-01', 100); +INSERT INTO stock VALUES ('company1', '2023-07-02', 200); +INSERT INTO stock VALUES ('company1', '2023-07-03', 150); +INSERT INTO stock VALUES ('company1', '2023-07-04', 140); +INSERT INTO stock VALUES ('company1', '2023-07-05', 150); +INSERT INTO stock VALUES ('company1', '2023-07-06', 90); +INSERT INTO stock VALUES ('company1', '2023-07-07', 110); +INSERT INTO stock VALUES ('company1', '2023-07-08', 130); +INSERT INTO stock VALUES ('company1', '2023-07-09', 120); +INSERT INTO stock VALUES ('company1', '2023-07-10', 130); +INSERT INTO stock VALUES ('company2', '2023-07-01', 50); +INSERT INTO stock VALUES ('company2', '2023-07-02', 2000); +INSERT INTO stock VALUES ('company2', '2023-07-03', 1500); +INSERT INTO stock VALUES ('company2', '2023-07-04', 1400); +INSERT INTO stock VALUES ('company2', '2023-07-05', 1500); +INSERT INTO stock VALUES ('company2', '2023-07-06', 60); +INSERT INTO stock VALUES ('company2', '2023-07-07', 1100); +INSERT INTO stock VALUES ('company2', '2023-07-08', 1300); +INSERT INTO stock VALUES ('company2', '2023-07-09', 1200); +INSERT INTO stock VALUES ('company2', '2023-07-10', 1300); + +SELECT * FROM stock; + +-- basic test using PREV +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- basic test using PREV. UP appears twice +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+ UP+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- basic test using PREV. Use '*' +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP* DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- basic test with none greedy pattern +SELECT company, tdate, price, count(*) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (A A A) + DEFINE + A AS price >= 140 AND price <= 150 +); + +-- last_value() should remain consistent +SELECT company, tdate, price, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- omit "START" in DEFINE but it is ok because "START AS TRUE" is +-- implicitly defined. per spec. +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w, + nth_value(tdate, 2) OVER w AS nth_second + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- the first row start with less than or equal to 100 +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (LOWPRICE UP+ DOWN+) + DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- second row raises 120% +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (LOWPRICE UP+ DOWN+) + DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price) * 1.2, + DOWN AS price < PREV(price) +); + +-- using NEXT +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UPDOWN) + DEFINE + START AS TRUE, + UPDOWN AS price > PREV(price) AND price > NEXT(price) +); + +-- using AFTER MATCH SKIP TO NEXT ROW +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP TO NEXT ROW + INITIAL + PATTERN (START UPDOWN) + DEFINE + START AS TRUE, + UPDOWN AS price > PREV(price) AND price > NEXT(price) +); + +-- match everything + +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + INITIAL + PATTERN (A+) + DEFINE + A AS TRUE +); + +-- backtracking with reclassification of rows +-- using AFTER MATCH SKIP PAST LAST ROW +SELECT company, tdate, price, first_value(tdate) OVER w, last_value(tdate) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + INITIAL + PATTERN (A+ B+) + DEFINE + A AS price > 100, + B AS price > 100 +); + +-- backtracking with reclassification of rows +-- using AFTER MATCH SKIP TO NEXT ROW +SELECT company, tdate, price, first_value(tdate) OVER w, last_value(tdate) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP TO NEXT ROW + INITIAL + PATTERN (A+ B+) + DEFINE + A AS price > 100, + B AS price > 100 +); + +-- ROWS BETWEEN CURRENT ROW AND offset FOLLOWING +SELECT company, tdate, price, first_value(tdate) OVER w, last_value(tdate) OVER w, + count(*) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- +-- Aggregates +-- + +-- using AFTER MATCH SKIP PAST LAST ROW +SELECT company, tdate, price, + first_value(price) OVER w, + last_value(price) OVER w, + max(price) OVER w, + min(price) OVER w, + sum(price) OVER w, + avg(price) OVER w, + count(price) OVER w +FROM stock +WINDOW w AS ( +PARTITION BY company +ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING +AFTER MATCH SKIP PAST LAST ROW +INITIAL +PATTERN (START UP+ DOWN+) +DEFINE +START AS TRUE, +UP AS price > PREV(price), +DOWN AS price < PREV(price) +); + +-- using AFTER MATCH SKIP TO NEXT ROW +SELECT company, tdate, price, + first_value(price) OVER w, + last_value(price) OVER w, + max(price) OVER w, + min(price) OVER w, + sum(price) OVER w, + avg(price) OVER w, + count(price) OVER w +FROM stock +WINDOW w AS ( +PARTITION BY company +ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING +AFTER MATCH SKIP TO NEXT ROW +INITIAL +PATTERN (START UP+ DOWN+) +DEFINE +START AS TRUE, +UP AS price > PREV(price), +DOWN AS price < PREV(price) +); + +-- JOIN case +CREATE TEMP TABLE t1 (i int, v1 int); +CREATE TEMP TABLE t2 (j int, v2 int); +INSERT INTO t1 VALUES(1,10); +INSERT INTO t1 VALUES(1,11); +INSERT INTO t1 VALUES(1,12); +INSERT INTO t2 VALUES(2,10); +INSERT INTO t2 VALUES(2,11); +INSERT INTO t2 VALUES(2,12); + +SELECT * FROM t1, t2 WHERE t1.v1 <= 11 AND t2.v2 <= 11; + +SELECT *, count(*) OVER w FROM t1, t2 +WINDOW w AS ( + PARTITION BY t1.i + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (A) + DEFINE + A AS v1 <= 11 AND v2 <= 11 +); + +-- WITH case +WITH wstock AS ( + SELECT * FROM stock WHERE tdate < '2023-07-08' +) +SELECT tdate, price, +first_value(tdate) OVER w, +count(*) OVER w + FROM wstock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- +-- Error cases +-- + +-- row pattern definition variable name must not appear more than once +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + ORDER BY tdate + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price), + UP AS price > PREV(price) +); + +-- pattern variable name must appear in DEFINE +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+ END) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- FRAME must start at current row when row patttern recognition is used +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING + INITIAL + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); + +-- SEEK is not supported +SELECT company, tdate, price, first_value(price) OVER w, last_value(price) OVER w + FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP TO NEXT ROW + SEEK + PATTERN (START UP+ DOWN+) + DEFINE + START AS TRUE, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); -- 2.25.1 ----Next_Part(Fri_Dec__8_10_16_13_2023_489)-- Content-Type: Text/X-Patch; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="v12-0007-Allow-to-print-raw-parse-tree.patch" ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <ah@cybertec.at> 0 siblings, 0 replies; 340+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 340+ messages in thread
end of thread, other threads:[~2026-04-14 09:59 UTC | newest] Thread overview: 340+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2023-12-04 11:23 [PATCH v12 6/7] Row pattern recognition patch (tests). Tatsuo Ishii <ishii@postgresql.org> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <ah@cybertec.at>
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