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Optimize PredicateLockTuple().

PredicateLockTuple() has a fast exit if tuple was written by the currenttransaction, as in that case it already has a lock. This check can beperformed using TransactionIdIsCurrentTransactionId() instead ofSubTransGetTopmostTransaction(), to avoid any chance of having to hit thedisk.Author: Ashwin Agrawal, based on a suggestion from Andres FreundReviewed-by: Thomas MunroDiscussion:https://postgr.es/m/CALfoeiv0k3hkEb3Oqk%3DziWqtyk2Jys1UOK5hwRBNeANT_yX%2Bng%40mail.gmail.com

1 parent695c597 commitdb2687dCopy full SHA for db2687d

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src/backend/storage/lmgr
- predicate.c

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`‎src/backend/storage/lmgr/predicate.c`

Lines changed: 3 additions & 19 deletions

Original file line number	Diff line number	Diff line change
`@@ -2549,7 +2549,6 @@ PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot)`
`2549`	`2549`	`{`
`2550`	`2550`	`PREDICATELOCKTARGETTAGtag;`
`2551`	`2551`	`ItemPointertid;`
`2552`		`-TransactionIdtargetxmin;`
`2553`	`2552`
`2554`	`2553`	`if (!SerializationNeededForRead(relation,snapshot))`
`2555`	`2554`	`return;`
`@@ -2559,24 +2558,9 @@ PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot)`
`2559`	`2558`	`*/`
`2560`	`2559`	`if (relation->rd_index==NULL)`
`2561`	`2560`	`{`
`2562`		`-TransactionIdmyxid;`
`2563`		`-`
`2564`		`-targetxmin=HeapTupleHeaderGetXmin(tuple->t_data);`
`2565`		`-`
`2566`		`-myxid=GetTopTransactionIdIfAny();`
`2567`		`-if (TransactionIdIsValid(myxid))`
`2568`		`-{`
`2569`		`-if (TransactionIdFollowsOrEquals(targetxmin,TransactionXmin))`
`2570`		`-{`
`2571`		`-TransactionIdxid=SubTransGetTopmostTransaction(targetxmin);`
`2572`		`-`
`2573`		`-if (TransactionIdEquals(xid,myxid))`
`2574`		`-{`
`2575`		`-/* We wrote it; we already have a write lock. */`
`2576`		`-return;`
`2577`		`-}`
`2578`		`-}`
`2579`		`-}`
	`2561`	`+/* If we wrote it; we already have a write lock. */`
	`2562`	`+if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tuple->t_data)))`
	`2563`	`+return;`
`2580`	`2564`	`}`
`2581`	`2565`
`2582`	`2566`	`/*`

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`‎src/backend/storage/lmgr/predicate.c`

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