From be667cf6cc50dbf790635b88934acc8a4bbb857e Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Wed, 16 Oct 2019 18:45:05 +1300 Subject: [PATCH] Fix bug that could try to freeze running multixacts. Commits 801c2dc7 and 801c2dc7 made it possible for vacuum to try to freeze a multixact that is still running. That was prevented by a check, but raised an error. Repair. Back-patch all the way. Author: Nathan Bossart, Jeremy Schneider Reported-by: Jeremy Schneider Reviewed-by: Jim Nasby, Thomas Munro Discussion: https://postgr.es/m/DAFB8AFF-2F05-4E33-AD7F-FF8B0F760C17%40amazon.com --- src/backend/commands/vacuum.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index e154507ecd..4b67b40b28 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -893,6 +893,7 @@ vacuum_set_xid_limits(Relation rel, int effective_multixact_freeze_max_age; TransactionId limit; TransactionId safeLimit; + MultiXactId oldestMxact; MultiXactId mxactLimit; MultiXactId safeMxactLimit; @@ -970,7 +971,8 @@ vacuum_set_xid_limits(Relation rel, Assert(mxid_freezemin >= 0); /* compute the cutoff multi, being careful to generate a valid value */ - mxactLimit = GetOldestMultiXactId() - mxid_freezemin; + oldestMxact = GetOldestMultiXactId(); + mxactLimit = oldestMxact - mxid_freezemin; if (mxactLimit < FirstMultiXactId) mxactLimit = FirstMultiXactId; @@ -984,7 +986,11 @@ vacuum_set_xid_limits(Relation rel, ereport(WARNING, (errmsg("oldest multixact is far in the past"), errhint("Close open transactions with multixacts soon to avoid wraparound problems."))); - mxactLimit = safeMxactLimit; + /* Use the safe limit, unless an older mxact is still running */ + if (MultiXactIdPrecedes(oldestMxact, safeMxactLimit)) + mxactLimit = oldestMxact; + else + mxactLimit = safeMxactLimit; } *multiXactCutoff = mxactLimit; -- 2.23.0