From cc318cc38614481cf5e95b7ddb30643e356b3f23 Mon Sep 17 00:00:00 2001 From: Sami Imseih Date: Wed, 9 Sep 2026 12:29:22 +0000 Subject: [PATCH v4 1/1] Fix WAIT FOR rejection errors WAIT FOR is documented as unsupported in transactions above READ COMMITTED, but the implementation only rejected that case after a transaction snapshot had already been taken. As a result, higher isolation levels could reach the generic snapshot-check error instead of failing with an error indicating that the isolation level is not supported. The same "active or registered snapshot" error also included an isolation-level explanation as DETAIL, which is wrong for READ COMMITTED cases such as a held cursor. Reject transaction-snapshot mode explicitly before checking for registered or active snapshots, so REPEATABLE READ and SERIALIZABLE fail with the right message and snapshot-holding READ COMMITTED cases report the snapshot-specific error. Add recovery coverage for both cases. --- src/backend/commands/wait.c | 13 ++++++++++-- src/test/recovery/t/049_wait_for_lsn.pl | 28 ++++++++++++++++++++----- 2 files changed, 34 insertions(+), 7 deletions(-) diff --git a/src/backend/commands/wait.c b/src/backend/commands/wait.c index 9ba4c75021e..7240ce08bb3 100644 --- a/src/backend/commands/wait.c +++ b/src/backend/commands/wait.c @@ -18,6 +18,7 @@ #include "access/xlog.h" #include "access/xlogrecovery.h" #include "access/xlogwait.h" +#include "access/xact.h" #include "catalog/pg_type_d.h" #include "commands/defrem.h" #include "commands/wait.h" @@ -147,6 +148,15 @@ ExecWaitStmt(ParseState *pstate, WaitStmt *stmt, bool isTopLevel, } } + /* + * WAIT FOR must not be run in a transaction that uses a transaction + * snapshot. + */ + if (IsolationUsesXactSnapshot()) + ereport(ERROR, + errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("WAIT FOR cannot be executed within a transaction with an isolation level higher than READ COMMITTED")); + /* * We are going to wait for the LSN. We should first care that we don't * hold a snapshot and correspondingly our MyProc->xmin is invalid. @@ -171,8 +181,7 @@ ExecWaitStmt(ParseState *pstate, WaitStmt *stmt, bool isTopLevel, if (HaveRegisteredOrActiveSnapshot()) ereport(ERROR, errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), - errmsg("WAIT FOR must be called without an active or registered snapshot"), - errdetail("WAIT FOR cannot be executed within a transaction with an isolation level higher than READ COMMITTED.")); + errmsg("WAIT FOR must be called without an active or registered snapshot")); /* * As the result we should hold no snapshot, and correspondingly our xmin diff --git a/src/test/recovery/t/049_wait_for_lsn.pl b/src/test/recovery/t/049_wait_for_lsn.pl index cb7d4d461de..934b2b121e6 100644 --- a/src/test/recovery/t/049_wait_for_lsn.pl +++ b/src/test/recovery/t/049_wait_for_lsn.pl @@ -262,9 +262,9 @@ unlike( "WAIT FOR LSN after savepoint rollback did not disconnect"); # 5. Check mode validation: standby modes error on primary, primary mode errors -# on standby, and primary_flush works on primary. Also check that WAIT FOR -# triggers an error if called within a function, procedure, anonymous DO block, -# or inside a transaction with an isolation level higher than READ COMMITTED. +# on standby. Also check that WAIT FOR triggers an error if called within a +# function, procedure, anonymous DO block, in a transaction with an isolation +# level higher than READ COMMITTED, or with an active or registered snapshot. # Test standby_flush on primary - should error $node_primary->psql( @@ -282,13 +282,31 @@ $node_standby->psql( ok($stderr =~ /recovery is in progress/, "get an error when running primary_flush on the standby"); +$node_standby->psql( + 'postgres', + "BEGIN ISOLATION LEVEL REPEATABLE READ; WAIT FOR LSN '${lsn3}';", + stderr => \$stderr); +ok($stderr =~ + /ERROR:\s+WAIT FOR cannot be executed within a transaction with an isolation level higher than READ COMMITTED/, + "get an error when running WAIT FOR in a transaction with an isolation level higher than READ COMMITTED" +); + $node_standby->psql( 'postgres', "BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT 1; WAIT FOR LSN '${lsn3}';", stderr => \$stderr); -ok( $stderr =~ +ok($stderr =~ + /ERROR:\s+WAIT FOR cannot be executed within a transaction with an isolation level higher than READ COMMITTED/, + "get an isolation-level error when running WAIT FOR after taking a transaction snapshot" +); + +$node_standby->psql( + 'postgres', + "BEGIN ISOLATION LEVEL READ COMMITTED; DECLARE c CURSOR FOR SELECT 1; WAIT FOR LSN '${lsn3}';", + stderr => \$stderr); +ok($stderr =~ /WAIT FOR must be called without an active or registered snapshot/, - "get an error when running in a transaction with an isolation level higher than REPEATABLE READ" + "get an error when running WAIT FOR with an active or registered snapshot" ); # Test wrapping WAIT FOR into function, procedure, and anonymous DO block -- -- 2.50.1