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Commit0dd6ff0

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Avoid some unnecessary block reads in WAL reader
When reading a new page internally and depending on the way the WALreader facility gets used by plugins, the current implementation of theWAL reader may finish by reading a block multiple times while it is notactually necessary as the requested data length may be equal to what hasbeen already read. This can happen for any size, but is more likely tohappen at the end of a page. This can cause performance penalties inplugins which rely on the block reads to be purely sequential, zlib notliking backward reads for example. The new behavior also shaves somecycles when doing recovery.Author: Arthur ZakirovReviewed-by: Andrey Lepikhov, Michael Paquier, Grigory SmolkinDiscussion:https://postgr.es/m/2ddf4a32-517e-d6f4-d992-4a63b6035bfd@postgrespro.ru
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‎src/backend/access/transam/xlogreader.c

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Original file line numberDiff line numberDiff line change
@@ -536,7 +536,7 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
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/* check whether we have all the requested data already */
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if (targetSegNo==state->readSegNo&&targetPageOff==state->readOff&&
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reqLen<state->readLen)
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reqLen <=state->readLen)
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returnstate->readLen;
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/*

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