From 080cf32d22317591cd8891c797a4d925cf1dbda2 Mon Sep 17 00:00:00 2001
From: Thomas Munro <tmunro@postgresql.org>
Date: Thu, 17 Oct 2019 09:59:21 +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 35f07f0369c..ed91d0e0e13 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -429,6 +429,7 @@ vacuum_set_xid_limits(Relation rel,
int effective_multixact_freeze_max_age;
TransactionId limit;
TransactionId safeLimit;
+ MultiXactId oldestMxact;
MultiXactId mxactLimit;
MultiXactId safeMxactLimit;
@@ -504,7 +505,8 @@ 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;
@@ -518,7 +520,11 @@ 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;
--
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