Fix WAIT FOR LSN cleanup on subtransaction abort

WAIT FOR LSN registers the current backend in shared memory before entering an
interruptible wait loop.  Top-level abort and backend exit already call
WaitLSNCleanup(), but subtransaction abort did not.  If an interrupt, such as
statement_timeout, occurred while waiting inside a savepoint, rolling back to
the savepoint left the backend marked as present in the WAIT FOR LSN heap.

Clean up WAIT FOR LSN state from AbortSubTransaction() as well, and add
a TAP test covering reuse of WAIT FOR LSN after a savepoint rollback.

Reported-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Discussion: https://postgr.es/m/CAJTYsWXDRwo-RVRaQgwxVcXgURVFeX8BKnijQrPiPcSCkDDX9A%40mail.gmail.com
Author: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Author: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 48bc90c967353470854c2101d247dd9ee449b6a8..5586fbe5b07c6428e180162f0500d313d9ffaef4 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -5289,6 +5289,11 @@ AbortSubTransaction(void)
         */
        LWLockReleaseAll();
 
+       /*
+        * Cleanup waiting for LSN if any.
+        */
+       WaitLSNCleanup();
+
        pgstat_report_wait_end();
        pgstat_progress_end_command();
 

diff --git a/src/backend/access/transam/xlogwait.c b/src/backend/access/transam/xlogwait.c
index 18f78338330bb02f0ad0a04bd53d68d8ef9b3c5f..582dde3b061281947dd9d3ff9eb66de63a6821cf 100644 (file)
--- a/src/backend/access/transam/xlogwait.c
+++ b/src/backend/access/transam/xlogwait.c
@@ -360,7 +360,7 @@ WaitLSNWakeup(WaitLSNType lsnType, XLogRecPtr currentLSN)
 }
 
 /*
- * Clean up LSN waiters for exiting process
+ * Clean up any LSN wait state for the current process.
  */
 void
 WaitLSNCleanup(void)

diff --git a/src/test/recovery/t/049_wait_for_lsn.pl b/src/test/recovery/t/049_wait_for_lsn.pl
index 9f8af351ba8b3a6017cbb39083a66cabcdaa9cde..bc216064714d0cfd2c880fb95b710fd3177cb776 100644 (file)
--- a/src/test/recovery/t/049_wait_for_lsn.pl
+++ b/src/test/recovery/t/049_wait_for_lsn.pl
@@ -213,6 +213,54 @@ $output = $node_standby->safe_psql(
        WAIT FOR LSN '${lsn3}' WITH (timeout '10ms', no_throw);]);
 ok($output eq "timeout", "WAIT FOR returns correct status after timeout");
 
+# 4a. Check that aborting a subtransaction during WAIT FOR LSN cleans up the
+# shared wait-state.  Poll pg_stat_activity before canceling the first WAIT
+# FOR to ensure that the backend has registered itself in the waiters heap.
+# After rolling back to the savepoint, a second WAIT FOR in the same backend
+# must be able to register itself again.
+my $subxact_lsn = $node_primary->safe_psql('postgres',
+       "SELECT pg_current_wal_insert_lsn() + 10000000000");
+my $subxact_appname = 'wait_for_lsn_subxact_cleanup';
+my $subxact_session =
+  $node_primary->background_psql('postgres', on_error_stop => 0);
+$subxact_session->query_until(
+       qr/start/, qq[
+       SET application_name = '$subxact_appname';
+       BEGIN;
+       SAVEPOINT wait_cleanup;
+       \\echo start
+       WAIT FOR LSN '${subxact_lsn}' WITH (MODE 'primary_flush');
+       ROLLBACK TO wait_cleanup;
+       WAIT FOR LSN '${subxact_lsn}'
+               WITH (MODE 'primary_flush', timeout '10ms', no_throw);
+       COMMIT;
+]);
+$node_primary->poll_query_until(
+       'postgres',
+       "SELECT count(*) = 1 FROM pg_stat_activity
+        WHERE application_name = '$subxact_appname'
+          AND wait_event = 'WaitForWalFlush'"
+) or die "WAIT FOR LSN did not enter the primary_flush wait path";
+my $subxact_cancelled = $node_primary->safe_psql(
+       'postgres',
+       "SELECT pg_cancel_backend(pid) FROM pg_stat_activity
+        WHERE application_name = '$subxact_appname'
+          AND wait_event = 'WaitForWalFlush'"
+);
+is($subxact_cancelled, 't', "canceled WAIT FOR LSN in subtransaction");
+$subxact_session->quit;
+chomp($subxact_session->{stdout});
+like(
+       $subxact_session->{stderr},
+       qr/canceling statement due to user request/,
+       "query cancel interrupted WAIT FOR LSN in subtransaction");
+is($subxact_session->{stdout},
+       "timeout", "second WAIT FOR LSN timed out after savepoint rollback");
+unlike(
+       $subxact_session->{stderr},
+       qr/server closed the connection unexpectedly/,
+       "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,