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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
This commit is contained in:
Thomas Munro 2019-10-17 09:59:21 +13:00
parent 0d21f919eb
commit 6bda2af039
1 changed files with 8 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/backend/commands/vacuum.c
View File

@ -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;