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Assign AccessExclusiveLocks against subxacts in Hot Standby

Previously AELs were registered against the top-level xid, which couldcause locks to be held much longer than necessary in some cases duringHot Standby replay. We now record locks directly against their appropriatexids. Requires few code changes because original code allowed for thissituation but didn’t fully implement it.Discussion: CAKJS1f9vJ841HY=wonnLVbfkTWGYWdPN72VMxnArcGCjF3SywA@mail.gmail.comAuthor: Simon Riggs and David Rowley

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src/backend/storage/ipc
- standby.c

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`‎src/backend/storage/ipc/standby.c`

Lines changed: 2 additions & 6 deletions

Original file line number	Diff line number	Diff line change
`@@ -590,10 +590,6 @@ StandbyLockTimeoutHandler(void)`
`590`	`590`	`* RelationLockList, so we can keep track of the various entries made by`
`591`	`591`	`* the Startup process's virtual xid in the shared lock table.`
`592`	`592`	`*`
`593`		`- * We record the lock against the top-level xid, rather than individual`
`594`		`- * subtransaction xids. This means AccessExclusiveLocks held by aborted`
`595`		`- * subtransactions are not released as early as possible on standbys.`
`596`		`- *`
`597`	`593`	`* List elements use type xl_rel_lock, since the WAL record type exactly`
`598`	`594`	`* matches the information that we need to keep track of.`
`599`	`595`	`*`
`@@ -1052,7 +1048,7 @@ LogAccessExclusiveLock(Oid dbOid, Oid relOid)`
`1052`	`1048`	`{`
`1053`	`1049`	`xl_standby_lockxlrec;`
`1054`	`1050`
`1055`		`-xlrec.xid=GetTopTransactionId();`
	`1051`	`+xlrec.xid=GetCurrentTransactionId();`
`1056`	`1052`
`1057`	`1053`	`/*`
`1058`	`1054`	`* Decode the locktag back to the original values, to avoid sending lots`
`@@ -1084,7 +1080,7 @@ LogAccessExclusiveLockPrepare(void)`
`1084`	`1080`	`* GetRunningTransactionLocks() might see a lock associated with an`
`1085`	`1081`	`* InvalidTransactionId which we later assert cannot happen.`
`1086`	`1082`	`*/`
`1087`		`-(void)GetTopTransactionId();`
	`1083`	`+(void)GetCurrentTransactionId();`
`1088`	`1084`	`}`
`1089`	`1085`
`1090`	`1086`	`/*`

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Commit49bff53

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`‎src/backend/storage/ipc/standby.c`

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