From 6cdbabf5f243d5227588df5bfd3f83018bcefb9a Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Thu, 22 Jun 2023 17:27:54 -0700 Subject: [PATCH v3 1/2] Release lock after encountering bogs row in vac_truncate_clog() When vac_truncate_clog() encounters bogus datfrozenxid / datminmxid values, it returns early. Unfortunately, until now, it did not releas WrapLimitsVacuumLock. If the backend later tries to acquire WrapLimitsVacuumLock, the session / autovacuum worker hangs in an uncancellable way. Similarly, other sessions will hang waiting for the lock. However, if the backend holding the lock exited or errored out for some reason, the lock was released. The bug was introduced as a side effect of 566372b3d643. It is interesting that there are no production reports of this problem. That is likely due to a mix of bugs leading to bogus values having gotten less common, process exit releasing locks and instances of hangs being hard to debug for "normal" users. Discussion: https://postgr.es/m/20230621221208.vhsqgduwfpzwxnpg@awork3.anarazel.de --- src/backend/commands/vacuum.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 57ca41add2f..841188f71c0 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -1893,12 +1893,16 @@ vac_truncate_clog(TransactionId frozenXID, ereport(WARNING, (errmsg("some databases have not been vacuumed in over 2 billion transactions"), errdetail("You might have already suffered transaction-wraparound data loss."))); + LWLockRelease(WrapLimitsVacuumLock); return; } /* chicken out if data is bogus in any other way */ if (bogus) + { + LWLockRelease(WrapLimitsVacuumLock); return; + } /* * Advance the oldest value for commit timestamps before truncating, so -- 2.38.0