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Commit7921927

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Reverse the search order in afterTriggerAddEvent().
When scanning existing AfterTriggerSharedData records in searchof a match to the event being queued, we were examining therecords from oldest to newest. But it makes more sense to dothe opposite. The newest record is likely to be from the currentquery, while the oldest is likely to be from some previous commandin the same transaction, which will likely have different details.There aren't expected to be very many active AfterTriggerSharedDatarecords at once, so that this change is unlikely to make anyspectacular difference. Still, having added a nontrivially-expensivebms_equal call to this loop yesterday, I feel a need to shave cycleswhere possible.Discussion:https://postgr.es/m/4166712.1737583961@sss.pgh.pa.us
1 parentb663b94 commit7921927

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‎src/backend/commands/trigger.c

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -4104,11 +4104,12 @@ afterTriggerAddEvent(AfterTriggerEventList *events,
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/*
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* Try to locate a matching shared-data record already in the chunk. If
4107-
* none, make a new one.
4107+
* none, make a new one. The search begins with the most recently added
4108+
* record, since newer ones are most likely to match.
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*/
4109-
for (newshared= ((AfterTriggerShared)chunk->endptr)-1;
4110-
(char*)newshared>=chunk->endfree;
4111-
newshared--)
4110+
for (newshared= (AfterTriggerShared)chunk->endfree;
4111+
(char*)newshared<chunk->endptr;
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newshared++)
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{
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/* compare fields roughly by probability of them being different */
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if (newshared->ats_tgoid==evtshared->ats_tgoid&&
@@ -4120,8 +4121,9 @@ afterTriggerAddEvent(AfterTriggerEventList *events,
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evtshared->ats_modifiedcols))
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break;
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}
4123-
if ((char*)newshared<chunk->endfree)
4124+
if ((char*)newshared>=chunk->endptr)
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{
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newshared= ((AfterTriggerShared)chunk->endfree)-1;
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*newshared=*evtshared;
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/* now we must make a suitably-long-lived copy of the bitmap */
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newshared->ats_modifiedcols=afterTriggerCopyBitmap(evtshared->ats_modifiedcols);

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