pg_logicalinspect: Stabilize isolation tests.

The previous isolation tests did not account for the possibility that
the background writer or the checkpointer could write a RUNNING_XACTS
record, which could cause logical decoding to produce more logical
snapshots than expected.

This commit modifies the isolation tests to verify that at least one
logical snapshot contains the expected number of committed or ongoing
catalog-change transactions.

Per buildfarm member skink.

Reported-by: Andres Freund <andres@anarazel.de>
Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/5qbxud4pvnvmtuoi7weiizm5hmumxaeohx4vztfhrwlfhyz6rj@buh4435mllwo

1 files changed, 18 insertions, 6 deletions

diff --git a/contrib/pg_logicalinspect/specs/logical_inspect.spec b/contrib/pg_logicalinspect/specs/logical_inspect.spec
index 9851a6c18e4..26b2db10f3e 100644
--- a/contrib/pg_logicalinspect/specs/logical_inspect.spec
+++ b/contrib/pg_logicalinspect/specs/logical_inspect.spec
@@ -1,9 +1,10 @@
 # Test the pg_logicalinspect functions: that needs some permutation to
-# ensure that we are creating multiple logical snapshots and that one of them
-# contains ongoing catalogs changes.
+# ensure that we are creating at least one snapshot that contains ongoing and
+# committed catalogs changes.
 setup
 {
     DROP TABLE IF EXISTS tbl1;
+    DROP TABLE IF EXISTS tbl2;
     CREATE TABLE tbl1 (val1 integer, val2 integer);
     CREATE EXTENSION pg_logicalinspect;
 }
@@ -11,6 +12,7 @@ setup
 teardown
 {
     DROP TABLE tbl1;
+    DROP TABLE tbl2;
     SELECT 'stop' FROM pg_drop_replication_slot('isolation_slot');
     DROP EXTENSION pg_logicalinspect;
 }
@@ -21,14 +23,24 @@ step "s0_init" { SELECT 'init' FROM pg_create_logical_replication_slot('isolatio
 step "s0_begin" { BEGIN; }
 step "s0_savepoint" { SAVEPOINT sp1; }
 step "s0_truncate" { TRUNCATE tbl1; }
-step "s0_insert" { INSERT INTO tbl1 VALUES (1); }
 step "s0_commit" { COMMIT; }
 
 session "s1"
 setup { SET synchronous_commit=on; }
 step "s1_checkpoint" { CHECKPOINT; }
+step "s1_create_table" { CREATE TABLE tbl2 (val1 integer, val2 integer); }
 step "s1_get_changes" { SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0'); }
-step "s1_get_logical_snapshot_meta" { SELECT COUNT(meta.*) from pg_ls_logicalsnapdir(), pg_get_logical_snapshot_meta(name) as meta;}
-step "s1_get_logical_snapshot_info" { SELECT info.state, info.catchange_count, array_length(info.catchange_xip,1) AS catchange_array_length, info.committed_count, array_length(info.committed_xip,1) AS committed_array_length FROM pg_ls_logicalsnapdir(), pg_get_logical_snapshot_info(name) AS info ORDER BY 2; }
+step "s1_check_snapshot_meta" { SELECT count(meta.*) > 0 AS has_meta from pg_ls_logicalsnapdir(), pg_get_logical_snapshot_meta(name) as meta; }
+step "s1_check_snapshot_info" { SELECT count(*) > 0 as has_info FROM pg_ls_logicalsnapdir(), pg_get_logical_snapshot_info(name) AS info where info.catchange_count >= 2 and array_length(info.catchange_xip,1) >= 2 and info.committed_count >= 1 and array_length(info.committed_xip,1) >= 1; }
 
-permutation "s0_init" "s0_begin" "s0_savepoint" "s0_truncate" "s1_checkpoint" "s1_get_changes" "s0_commit" "s0_begin" "s0_insert" "s1_checkpoint" "s1_get_changes" "s0_commit" "s1_get_changes" "s1_get_logical_snapshot_info" "s1_get_logical_snapshot_meta"
+
+# Both s0 and s1 execute catalog-change transactions. When "s1_get_changes" is
+# executed, s0's transaction is still in progress, while s1's transaction has
+# already completed. Consequently, the logical decoding produces a snapshot at
+# the point where a RUNNING_XACTS record is generated by "s1_checkpoint".
+# This snapshot contains both two ongoing catalog-change transactions (from s0's
+# top-level and sub transactions) and one completed transaction (from s1).
+# "s1_check_snapshot_info" verifies whether the logical snapshot contains at
+# least the expected number of transactions, accounting for potential
+# additional catalog changes that may occur due to concurrent autoanalyze.
+permutation "s0_init" "s0_begin" "s0_savepoint" "s0_truncate" "s1_create_table" "s1_checkpoint" "s1_get_changes" "s1_check_snapshot_info" "s1_check_snapshot_meta" "s0_commit"