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Commitfbc0d07

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Partially roll back overenthusiastic SSI optimization.
When a regular lock is held, SSI can use that in lieu of a predicate lockto detect rw conflicts; but if the regular lock is being taken by asubtransaction, we can't assume that it'll commit, so releasing theparent transaction's lock in that case is a no-no.Kevin Grittner
1 parent9c38bce commitfbc0d07

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1 file changed

+13
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‎src/backend/storage/lmgr/predicate.c

Lines changed: 13 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -3638,14 +3638,20 @@ CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
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if (sxact==MySerializableXact)
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{
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/*
3641-
* If we're getting a write lock on the tuple, we don't need a
3642-
* predicate (SIREAD) lock. At this point our transaction already
3643-
* has an ExclusiveRowLock on the relation, so we are OK to drop
3644-
* the predicate lock on the tuple, if found, without fearing that
3645-
* another write against the tuple will occur before the MVCC
3646-
* information makes it to the buffer.
3641+
* If we're getting a write lock on the tuple and we're not in a
3642+
* subtransaction, we don't need a predicate (SIREAD) lock. We
3643+
* can't use this optimization within a subtransaction because
3644+
* the subtransaction could be rolled back, and we would be left
3645+
* without any lock at the top level.
3646+
*
3647+
* At this point our transaction already has an ExclusiveRowLock
3648+
* on the relation, so we are OK to drop the predicate lock on
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* the tuple, if found, without fearing that another write
3650+
* against the tuple will occur before the MVCC information
3651+
* makes it to the buffer.
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*/
3648-
if (GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag))
3653+
if (!IsSubTransaction()
3654+
&&GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag))
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{
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uint32predlockhashcode;
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PREDICATELOCKTARGET*rmtarget=NULL;

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