Hi,
I got an assert failure when executing pg_terminate_backend to the
process that waiting for WAL to be archived in non-exclusive backup
mode.
TRAP: FailedAssertion("!(XLogCtl->Insert.nonExclusiveBackups > 0)",
File: "xlog.c", Line: 11123)
The one reproducing procedure is,
1. Start postgres with enabling the WAL archive
2. Execute pg_start_backup()
3. Revoke the access privileges of archive directory. (e.g., chown
root:root /path/to/archive)
4. Execute pg_stop_backup() and hangs
5. Execute pg_terminate_backend() to the process that is waiting for
WAL to be archived.
Got the assertion failure.
Perhaps we can reproduce it using pg_basebackup as well.
I think the cause of this is that do_pg_abort_backup can be called
even after we decremented XLogCtl->Insert.nonExclusiveBackups in
do_pg_stop_backup(). That is, do_pg_abort_backup can be called with
XLogCtl->Insert.nonExclusiveBackups = 0 when the transaction aborts
after processed the nonExclusiveBackups (e.g, during waiting for WAL
to be archived)
The bug can happen in PostgreSQL 9.1 or higher that non-exclusive
backup has been introduced, so we should back-patch to the all
supported versions.
I changed do_pg_abort_backup() so that it decrements
nonExclusiveBackups only if > 0. Feedback is very welcome.
Regards,
--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 0513471..b0381e8 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -11165,8 +11165,15 @@ void
do_pg_abort_backup(void)
{
WALInsertLockAcquireExclusive();
- Assert(XLogCtl->Insert.nonExclusiveBackups > 0);
- XLogCtl->Insert.nonExclusiveBackups--;
+
+ /*
+ * This can be called after we decremented nonExclusiveBackups in
+ * do_pg_stop_backup. So prevent it to be negative value.
+ */
+- Assert(XLogCtl->Insert.nonExclusiveBackups >= 0);
+ if (XLogCtl->Insert.nonExclusiveBackups > 0)
+ XLogCtl->Insert.nonExclusiveBackups--;
+
if (XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_NONE &&
XLogCtl->Insert.nonExclusiveBackups == 0)
--
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