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Commit04e6d3b

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Even when autovacuum=off, force it for members as we do in other cases.
Thomas Munro, with some adjustments by me.
1 parentf6a6c46 commit04e6d3b

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1 file changed

+52
-9
lines changed

1 file changed

+52
-9
lines changed

‎src/backend/access/transam/multixact.c

Lines changed: 52 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -204,6 +204,7 @@ typedef struct MultiXactStateData
204204
*/
205205
MultiXactIdoldestMultiXactId;
206206
OidoldestMultiXactDB;
207+
MultiXactOffsetoldestOffset;
207208

208209
/*
209210
* This is what the previous checkpoint stored as the truncate position.
@@ -954,14 +955,17 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
954955
* against catastrophic data loss due to multixact wraparound. The basic
955956
* rules are:
956957
*
957-
* If we're past multiVacLimit, start trying to force autovacuum cycles.
958+
* If we're past multiVacLimit or the safe threshold for member storage space,
959+
* start trying to force autovacuum cycles.
958960
* If we're past multiWarnLimit, start issuing warnings.
959961
* If we're past multiStopLimit, refuse to create new MultiXactIds.
960962
*
961963
* Note these are pretty much the same protections in GetNewTransactionId.
962964
*----------
963965
*/
964-
if (!MultiXactIdPrecedes(result,MultiXactState->multiVacLimit))
966+
if (!MultiXactIdPrecedes(result,MultiXactState->multiVacLimit)||
967+
(MultiXactState->nextOffset-MultiXactState->oldestOffset
968+
>MULTIXACT_MEMBER_SAFE_THRESHOLD))
965969
{
966970
/*
967971
* For safety's sake, we release MultiXactGenLock while sending
@@ -2142,6 +2146,8 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
21422146
MultiXactIdmultiStopLimit;
21432147
MultiXactIdmultiWrapLimit;
21442148
MultiXactIdcurMulti;
2149+
MultiXactOffsetoldestOffset;
2150+
MultiXactOffsetnextOffset;
21452151

21462152
Assert(MultiXactIdIsValid(oldest_datminmxid));
21472153

@@ -2194,6 +2200,35 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
21942200
if (multiVacLimit<FirstMultiXactId)
21952201
multiVacLimit+=FirstMultiXactId;
21962202

2203+
/*
2204+
* Determine the offset of the oldest multixact that might still be
2205+
* referenced. Normally, we can read the offset from the multixact itself,
2206+
* but there's an important special case: if there are no multixacts in
2207+
* existence at all, oldest_datminmxid obviously can't point to one. It
2208+
* will instead point to the multixact ID that will be assigned the next
2209+
* time one is needed.
2210+
*
2211+
* NB: oldest_dataminmxid is the oldest multixact that might still be
2212+
* referenced from a table, unlike in DetermineSafeOldestOffset, where we
2213+
* do this same computation based on the oldest value that might still
2214+
* exist in the SLRU. This is because here we're trying to compute a
2215+
* threshold for activating autovacuum, which can only remove references
2216+
* to multixacts, whereas there we are computing a threshold for creating
2217+
* new multixacts, which requires the old ones to have first been
2218+
* truncated away by a checkpoint.
2219+
*/
2220+
LWLockAcquire(MultiXactGenLock,LW_SHARED);
2221+
if (MultiXactState->nextMXact==oldest_datminmxid)
2222+
{
2223+
oldestOffset=MultiXactState->nextOffset;
2224+
LWLockRelease(MultiXactGenLock);
2225+
}
2226+
else
2227+
{
2228+
LWLockRelease(MultiXactGenLock);
2229+
oldestOffset=find_multixact_start(oldest_datminmxid);
2230+
}
2231+
21972232
/* Grab lock for just long enough to set the new limit values */
21982233
LWLockAcquire(MultiXactGenLock,LW_EXCLUSIVE);
21992234
MultiXactState->oldestMultiXactId=oldest_datminmxid;
@@ -2202,7 +2237,9 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
22022237
MultiXactState->multiWarnLimit=multiWarnLimit;
22032238
MultiXactState->multiStopLimit=multiStopLimit;
22042239
MultiXactState->multiWrapLimit=multiWrapLimit;
2240+
MultiXactState->oldestOffset=oldestOffset;
22052241
curMulti=MultiXactState->nextMXact;
2242+
nextOffset=MultiXactState->nextOffset;
22062243
LWLockRelease(MultiXactGenLock);
22072244

22082245
/* Log the info */
@@ -2217,7 +2254,8 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
22172254
* database, it'll call here, and we'll signal the postmaster to start
22182255
* another iteration immediately if there are still any old databases.
22192256
*/
2220-
if (MultiXactIdPrecedes(multiVacLimit,curMulti)&&
2257+
if ((MultiXactIdPrecedes(multiVacLimit,curMulti)||
2258+
(nextOffset-oldestOffset>MULTIXACT_MEMBER_SAFE_THRESHOLD))&&
22212259
IsUnderPostmaster&& !InRecovery)
22222260
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
22232261

@@ -2476,11 +2514,16 @@ DetermineSafeOldestOffset(MultiXactId oldestMXact)
24762514
MultiXactOffsetoldestOffset;
24772515

24782516
/*
2479-
* We determine the safe upper bound for offsets of new xacts by reading
2480-
* the offset of the oldest multixact, and going back one segment. This
2481-
* way, the sequence of multixact member segments will always have a
2482-
* one-segment hole at a minimum. We start spewing warnings a few
2483-
* complete segments before that.
2517+
* Determine the offset of the oldest multixact. Normally, we can read
2518+
* the offset from the multixact itself, but there's an important special
2519+
* case: if there are no multixacts in existence at all, oldestMXact
2520+
* obviously can't point to one. It will instead point to the multixact
2521+
* ID that will be assigned the next time one is needed.
2522+
*
2523+
* NB: oldestMXact should be the oldest multixact that still exists in
2524+
* the SLRU, unlike in SetMultiXactIdLimit, where we do this same
2525+
* computation based on the oldest value that might be referenced in a
2526+
* table.
24842527
*/
24852528
LWLockAcquire(MultiXactGenLock,LW_SHARED);
24862529
if (MultiXactState->nextMXact==oldestMXact)
@@ -2594,9 +2637,9 @@ ReadMultiXactCounts(uint32 *multixacts, MultiXactOffset *members)
25942637
nextOffset=MultiXactState->nextOffset;
25952638
oldestMultiXactId=MultiXactState->oldestMultiXactId;
25962639
nextMultiXactId=MultiXactState->nextMXact;
2640+
oldestOffset=MultiXactState->oldestOffset;
25972641
LWLockRelease(MultiXactGenLock);
25982642

2599-
oldestOffset=find_multixact_start(oldestMultiXactId);
26002643
*members=nextOffset-oldestOffset;
26012644
*multixacts=nextMultiXactId-oldestMultiXactId;
26022645
}

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