Subject: [PATCH v5 1/3] Test for snapshot too old and wal_level=minimal

From: Kyotaro Horiguchi <[email-masked]>
Date: Wed, 20 Jan 2021 20:57:03 +0900

---
 src/test/modules/snapshot_too_old/Makefile    | 12 ++++-
 .../expected/sto_wal_optimized.out            | 24 ++++++++++
 .../input_sto/sto_wal_optimized.spec          | 44 +++++++++++++++++++
 src/test/modules/snapshot_too_old/sto.conf    |  3 ++
 4 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 src/test/modules/snapshot_too_old/expected/sto_wal_optimized.out
 create mode 100644 src/test/modules/snapshot_too_old/input_sto/sto_wal_optimized.spec

diff --git a/src/test/modules/snapshot_too_old/Makefile b/src/test/modules/snapshot_too_old/Makefile
index dfb4537f63..1e0b0b6efc 100644
--- a/src/test/modules/snapshot_too_old/Makefile
+++ b/src/test/modules/snapshot_too_old/Makefile
@@ -4,7 +4,7 @@
 # we have to clean those result files explicitly
 EXTRA_CLEAN = $(pg_regress_clean_files)
 
-ISOLATION = sto_using_cursor sto_using_select sto_using_hash_index
+ISOLATION = sto_using_cursor sto_using_select sto_using_hash_index sto_wal_optimized
 ISOLATION_OPTS = --temp-config $(top_srcdir)/src/test/modules/snapshot_too_old/sto.conf
 
 # Disabled because these tests require "old_snapshot_threshold" >= 0, which
@@ -22,6 +22,16 @@ include $(top_builddir)/src/Makefile.global
 include $(top_srcdir)/contrib/contrib-global.mk
 endif
 
+.PHONY: tablespace-setup specfile-setup
+tablespace-setup:
+	rm -rf ./testtablespace
+	mkdir ./testtablespace
+
+specfile-setup: input_sto/*.spec
+	sed 's!@srcdir@!$(realpath $(top_srcdir))!g' $? > specs/$(notdir $?)
+
+check: tablespace-setup specfile-setup
+
 # But it can nonetheless be very helpful to run tests on preexisting
 # installation, allow to do so, but only if requested explicitly.
 installcheck-force:
diff --git a/src/test/modules/snapshot_too_old/expected/sto_wal_optimized.out b/src/test/modules/snapshot_too_old/expected/sto_wal_optimized.out
new file mode 100644
index 0000000000..4038d0a713
--- /dev/null
+++ b/src/test/modules/snapshot_too_old/expected/sto_wal_optimized.out
@@ -0,0 +1,24 @@
+Parsed test spec with 3 sessions
+
+starting permutation: s1a1 s1a2 s2a1 s2a2 s1b1 a3-0 a3-1 s3-2 s3-3 s3-4 s2b1
+step s1a1: BEGIN;
+step s1a2: DELETE FROM t;
+step s2a1: BEGIN ISOLATION LEVEL REPEATABLE READ;
+step s2a2: SELECT 1;
+?column?       
+
+1              
+step s1b1: COMMIT;
+step a3-0: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
+setting        pg_sleep       
+
+0                             
+step a3-1: BEGIN;
+step s3-2: ALTER TABLE t SET TABLESPACE tsp1;
+step s3-3: SELECT count(*) FROM t;
+count          
+
+0              
+step s3-4: COMMIT;
+step s2b1: SELECT count(*) FROM t;
+ERROR:  snapshot too old
diff --git a/src/test/modules/snapshot_too_old/input_sto/sto_wal_optimized.spec b/src/test/modules/snapshot_too_old/input_sto/sto_wal_optimized.spec
new file mode 100644
index 0000000000..02adb50581
--- /dev/null
+++ b/src/test/modules/snapshot_too_old/input_sto/sto_wal_optimized.spec
@@ -0,0 +1,44 @@
+# This test provokes a "snapshot too old" error 
+#
+# The sleep is needed because with a threshold of zero a statement could error
+# on changes it made.  With more normal settings no external delay is needed,
+# but we don't want these tests to run long enough to see that, since
+# granularity is in minutes.
+#
+# Since results depend on the value of old_snapshot_threshold, sneak that into
+# the line generated by the sleep, so that a surprising values isn't so hard
+# to identify.
+
+setup
+{
+	CREATE TABLESPACE tsp1 LOCATION '@srcdir@/src/test/modules/snapshot_too_old/testtablespace';
+}
+
+setup
+{
+	CREATE TABLE t AS SELECT a FROM generate_series(0, 9) a;
+}
+
+session "s1"
+step "s1a1" { BEGIN; }
+step "s1a2" { DELETE FROM t; }
+step "s1b1" { COMMIT; }
+
+session "s2"
+# s2a : take snapshot
+step "s2a1" { BEGIN ISOLATION LEVEL REPEATABLE READ; }
+step "s2a2" { SELECT 1; }
+# s2b : wanted "snapshot too old"
+step "s2b1" { SELECT count(*) FROM t; }
+
+session "s3"
+# s3-0 : wait for snapshot is expired
+step "a3-0"   { SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold'; }
+step "a3-1"   { BEGIN; }
+# s3-2 : start skipping WAL when wal_level=minimal
+step "s3-2"   { ALTER TABLE t SET TABLESPACE tsp1; }
+# s3-3 : early pruning. w/o WAL and LSN changes when wal_level=minimal
+step "s3-3"   { SELECT count(*) FROM t; }
+step "s3-4"   { COMMIT; }
+
+permutation "s1a1" "s1a2" "s2a1" "s2a2" "s1b1" "a3-0" "a3-1" "s3-2" "s3-3" "s3-4" "s2b1"
diff --git a/src/test/modules/snapshot_too_old/sto.conf b/src/test/modules/snapshot_too_old/sto.conf
index 7eeaeeb0dc..09887fc725 100644
--- a/src/test/modules/snapshot_too_old/sto.conf
+++ b/src/test/modules/snapshot_too_old/sto.conf
@@ -1,2 +1,5 @@
 autovacuum = off
 old_snapshot_threshold = 0
+
+# needed when setting wal_level=minimal
+wal_skip_threshold = 0
-- 
2.27.0

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 filename="v5-0002-Do-not-use-RelationNeedsWAL-to-identify-relation-.patch"