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Commit1a3d104

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Avoid acquiring spinlock when checking if recovery has finished, for speed.
RecoveryIsInProgress() can be called very frequently. During normaloperation, it just checks a backend-local variable and returns quickly,but during hot standby, it checks a spinlock-protected shared variable.Those spinlock acquisitions can become a point of contention on a busyhot standby system.Replace the spinlock acquisition with a memory barrier.Per discussion with Andres Freund, Ants Aasma and Merlin Moncure.
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  • src/backend/access/transam

1 file changed

+17
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‎src/backend/access/transam/xlog.c

100644100755
Lines changed: 17 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -7367,13 +7367,13 @@ RecoveryInProgress(void)
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return false;
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else
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{
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/* use volatile pointer to prevent code rearrangement */
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/*
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* use volatile pointer to make sure we make a fresh read of the
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* shared variable.
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*/
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volatileXLogCtlData*xlogctl=XLogCtl;
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7373-
/* spinlock is essential on machines with weak memory ordering! */
7374-
SpinLockAcquire(&xlogctl->info_lck);
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LocalRecoveryInProgress=xlogctl->SharedRecoveryInProgress;
7376-
SpinLockRelease(&xlogctl->info_lck);
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/*
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* Initialize TimeLineID and RedoRecPtr when we discover that recovery
@@ -7382,7 +7382,20 @@ RecoveryInProgress(void)
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* this, see also LocalSetXLogInsertAllowed.)
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*/
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if (!LocalRecoveryInProgress)
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{
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/*
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* If we just exited recovery, make sure we read TimeLineID and
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* RedoRecPtr after SharedRecoveryInProgress (for machines with
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* weak memory ordering).
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*/
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pg_memory_barrier();
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InitXLOGAccess();
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}
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/*
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* Note: We don't need a memory barrier when we're still in recovery.
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* We might exit recovery immediately after return, so the caller
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* can't rely on 'true' meaning that we're still in recovery anyway.
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*/
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returnLocalRecoveryInProgress;
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}

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