Commit2f39106

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Replace CAS loop with single TAS in ProcArrayGroupClearXid()

Single pg_atomic_exchange_u32() is expected to be faster than loop ofpg_atomic_compare_exchange_u32(). Also, it would be consistent withclog group update code.Discussion:https://postgr.es/m/CAPpHfdtxLsC-bqfxFcHswZ91OxXcZVNDBBVfg9tAWU0jvn1tQA%40mail.gmail.comReviewed-by: Amit Kapila

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Lines changed: 2 additions & 8 deletions

Original file line number	Diff line number	Diff line change
`@@ -542,14 +542,8 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)`
`542`	`542`	`* group XID clearing, saving a pointer to the head of the list. Trying`
`543`	`543`	`* to pop elements one at a time could lead to an ABA problem.`
`544`	`544`	`*/`
`545`		`-while (true)`
`546`		`-{`
`547`		`-nextidx=pg_atomic_read_u32(&procglobal->procArrayGroupFirst);`
`548`		`-if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,`
`549`		`-&nextidx,`
`550`		`-INVALID_PGPROCNO))`
`551`		`-break;`
`552`		`-}`
	`545`	`+nextidx=pg_atomic_exchange_u32(&procglobal->procArrayGroupFirst,`
	`546`	`+INVALID_PGPROCNO);`
`553`	`547`
`554`	`548`	`/* Remember head of list so we can perform wakeups after dropping lock. */`
`555`	`549`	`wakeidx=nextidx;`

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