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Commit24ace40

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Retry after buffer locking failure during SPGiST index creation.
The original coding thought this case was impossible, but it can happenif the bgwriter or checkpointer processes decide to write out an indexpage while creation is still proceeding, leading to a bogus "unexpectedspgdoinsert() failure" error. Problem reported by Jonathan S. Katz.Teodor Sigaev
1 parentbffd1ce commit24ace40

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2 files changed

+17
-7
lines changed

2 files changed

+17
-7
lines changed

‎src/backend/access/spgist/spgdoinsert.c

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1946,9 +1946,12 @@ spgdoinsert(Relation index, SpGistState *state,
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* Attempt to acquire lock on child page. We must beware of
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* deadlock against another insertion process descending from that
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* page to our parent page (see README). If we fail to get lock,
1949-
* abandon the insertion and tell our caller to start over. XXX
1950-
* this could be improved; perhaps it'd be worth sleeping a bit
1951-
* before giving up?
1949+
* abandon the insertion and tell our caller to start over.
1950+
*
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* XXX this could be improved, because failing to get lock on a
1952+
* buffer is not proof of a deadlock situation; the lock might be
1953+
* held by a reader, or even just background writer/checkpointer
1954+
* process. Perhaps it'd be worth retrying after sleeping a bit?
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*/
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if (!ConditionalLockBuffer(current.buffer))
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{

‎src/backend/access/spgist/spginsert.c

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -45,10 +45,17 @@ spgistBuildCallback(Relation index, HeapTuple htup, Datum *values,
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/* Work in temp context, and reset it after each tuple */
4646
oldCtx=MemoryContextSwitchTo(buildstate->tmpCtx);
4747

48-
/* No concurrent insertions can be happening, so failure is unexpected */
49-
if (!spgdoinsert(index,&buildstate->spgstate,&htup->t_self,
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*values,*isnull))
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elog(ERROR,"unexpected spgdoinsert() failure");
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/*
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* Even though no concurrent insertions can be happening, we still might
50+
* get a buffer-locking failure due to bgwriter or checkpointer taking a
51+
* lock on some buffer. So we need to be willing to retry. We can flush
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* any temp data when retrying.
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*/
54+
while (!spgdoinsert(index,&buildstate->spgstate,&htup->t_self,
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*values,*isnull))
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{
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MemoryContextReset(buildstate->tmpCtx);
58+
}
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5360
MemoryContextSwitchTo(oldCtx);
5461
MemoryContextReset(buildstate->tmpCtx);

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