postgres.git / summary / log / commit / refs

commit    f5f9a760a3bc2be95f8716e476150ce128efa22b
Author:   Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:     Tue Feb 12 21:42:37 2019 +0000
First released in: 12.0, 9.4.22, 9.5.17, 9.6.13, 10.8, 11.3

    Relax overly strict assertion
    
    Ever since its birth, ReorderBufferBuildTupleCidHash() has contained an
    assertion that a catalog tuple cannot change Cmax after acquiring one.  But
    that's wrong: if a subtransaction executes DDL that affects that catalog
    tuple, and later aborts and another DDL affects the same tuple, it will
    change Cmax.  Relax the assertion to merely verify that the Cmax remains
    valid and monotonically increasing, instead.
    
    Add a test that tickles the relevant code.
    
    Diagnosed by, and initial patch submitted by: Arseny Sher
    Co-authored-by: Arseny Sher
    Discussion: https://postgr.es/m/874l9p8hyw.fsf@ars-thinkpad


 contrib/test_decoding/expected/ddl.out          | 18 ++++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               | 13 +++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 14 +++++++++-----
 3 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 1e22c1eefc1..a5292c358aa 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -405,6 +405,24 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
  COMMIT
 (6 rows)
 
+-- check that DDL in aborted subtransactions handled correctly
+CREATE TABLE tr_sub_ddl(data int);
+BEGIN;
+SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
+INSERT INTO tr_sub_ddl VALUES ('blah-blah');
+ROLLBACK TO SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
+INSERT INTO tr_sub_ddl VALUES(43);
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+                       data                       
+--------------------------------------------------
+ BEGIN
+ table public.tr_sub_ddl: INSERT: data[bigint]:43
+ COMMIT
+(3 rows)
+
 /*
  * Check whether treating a table as a catalog table works somewhat
  */
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index 057dae056be..6a3e33e0810 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -235,6 +235,19 @@ INSERT INTO tr_sub(path) VALUES ('5-top-1-#1');
 COMMIT;
 
 
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+
+-- check that DDL in aborted subtransactions handled correctly
+CREATE TABLE tr_sub_ddl(data int);
+BEGIN;
+SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
+INSERT INTO tr_sub_ddl VALUES ('blah-blah');
+ROLLBACK TO SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
+INSERT INTO tr_sub_ddl VALUES(43);
+COMMIT;
+
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 518703141fa..392757001f9 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -1334,15 +1334,19 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
 		}
 		else
 		{
+			/*
+			 * Maybe we already saw this tuple before in this transaction,
+			 * but if so it must have the same cmin.
+			 */
 			Assert(ent->cmin == change->data.tuplecid.cmin);
-			Assert(ent->cmax == InvalidCommandId ||
-				   ent->cmax == change->data.tuplecid.cmax);
 
 			/*
-			 * if the tuple got valid in this transaction and now got deleted
-			 * we already have a valid cmin stored. The cmax will be
-			 * InvalidCommandId though.
+			 * cmax may be initially invalid, but once set it can only grow,
+			 * and never become invalid again.
 			 */
+			Assert((ent->cmax == InvalidCommandId) ||
+				   ((change->data.tuplecid.cmax != InvalidCommandId) &&
+					(change->data.tuplecid.cmax > ent->cmax)));
 			ent->cmax = change->data.tuplecid.cmax;
 		}
 	}


[parent: 2a0edae47af4]