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Add comment about memory reordering to PredicateLockTupleRowVersionLink.

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Dan Ports, per head-scratching from Simon Riggs and myself.
This commit is contained in:
Robert Haas
2011-05-06 21:53:55 -04:00
parent 5c5f83507c
commit 71932ecc2b
1 changed files with 3 additions and 0 deletions
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3
src/backend/storage/lmgr/predicate.c
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@ -2283,6 +2283,9 @@ PredicateLockTupleRowVersionLink(const Relation relation,
* locks. Even if a serializable transaction starts concurrently, * locks. Even if a serializable transaction starts concurrently,
* we know it can't take any SIREAD locks on the modified tuple * we know it can't take any SIREAD locks on the modified tuple
* because the caller is holding the associated buffer page lock. * because the caller is holding the associated buffer page lock.
* Memory reordering isn't an issue; the memory barrier in the
* LWLock acquisition guarantees that this read occurs while the
* buffer page lock is held.
*/ */
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)) if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
return; return;