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Fix bug that could try to freeze running multixacts.

author Thomas Munro <tmunro@postgresql.org>

2019年10月16日 20:59:21 +0000 (09:59 +1300)

committer Thomas Munro <tmunro@postgresql.org>

2019年10月16日 20:59:21 +0000 (09:59 +1300)

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 patch | blob | blame | history

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c

index e154507ecd07ee8d3bdc4718b12d75fc8ccb7ad6..4b67b40b2858320567d50c9969b288730d62c2de 100644 (file)

--- 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;

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