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Optimize PredicateLockTuple().

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PredicateLockTuple() has a fast exit if tuple was written by the current
transaction, as in that case it already has a lock.  This check can be
performed using TransactionIdIsCurrentTransactionId() instead of
SubTransGetTopmostTransaction(), to avoid any chance of having to hit the
disk.

Author: Ashwin Agrawal, based on a suggestion from Andres Freund
Reviewed-by: Thomas Munro
Discussion: https://postgr.es/m/CALfoeiv0k3hkEb3Oqk%3DziWqtyk2Jys1UOK5hwRBNeANT_yX%2Bng%40mail.gmail.com
This commit is contained in:
Thomas Munro 2019-11-11 16:34:01 +13:00
parent 695c5977c8
commit db2687d1f3
1 changed files with 3 additions and 19 deletions
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20
src/backend/storage/lmgr/predicate.c
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@ -2549,7 +2549,6 @@ PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot)
{ {
PREDICATELOCKTARGETTAG tag; PREDICATELOCKTARGETTAG tag;
ItemPointer tid; ItemPointer tid;
TransactionId targetxmin;
if (!SerializationNeededForRead(relation, snapshot)) if (!SerializationNeededForRead(relation, snapshot))
return; return;
@ -2559,25 +2558,10 @@ PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot)
*/ */
if (relation->rd_index == NULL) if (relation->rd_index == NULL)
{ {
TransactionId myxid; /* If we wrote it; we already have a write lock. */
if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tuple->t_data)))
targetxmin = HeapTupleHeaderGetXmin(tuple->t_data);
myxid = GetTopTransactionIdIfAny();
if (TransactionIdIsValid(myxid))
{
if (TransactionIdFollowsOrEquals(targetxmin, TransactionXmin))
{
TransactionId xid = SubTransGetTopmostTransaction(targetxmin);
if (TransactionIdEquals(xid, myxid))
{
/* We wrote it; we already have a write lock. */
return; return;
} }
}
}
}
/* /*
* Do quick-but-not-definitive test for a relation lock first. This will * Do quick-but-not-definitive test for a relation lock first. This will