From 0a05391095185b5939b32d1d28b210d47c2bd597 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Thu, 22 Jun 2023 17:27:54 -0700 Subject: [PATCH v4 1/3] 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 57ca41add2..841188f71c 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 -- 2.32.1 (Apple Git-133)