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Don't count zero-filled buffers as 'read' in EXPLAIN.

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If you extend a relation, it should count as a block written, not
read (we write a zero-filled block).  If you ask for a zero-filled
buffer, it shouldn't be counted as read or written.

Later we might consider counting zero-filled buffers with a separate
counter, if they become more common due to future work.

Author: Thomas Munro
Reviewed-by: Haribabu Kommi, Kyotaro Horiguchi, David Rowley
Discussion: https://postgr.es/m/CAEepm%3D3JytB3KPpvSwXzkY%2Bdwc5zC8P8Lk7Nedkoci81_0E9rA%40mail.gmail.com
This commit is contained in:
Thomas Munro
2018-11-28 11:42:32 +13:00
parent 471a7af585
commit d67dae036b
1 changed files with 8 additions and 2 deletions
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10
src/backend/storage/buffer/bufmgr.c
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@ -733,7 +733,10 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, &found);
if (found)
pgBufferUsage.local_blks_hit++;
else
else if (isExtend)
pgBufferUsage.local_blks_written++;
else if (mode == RBM_NORMAL || mode == RBM_NORMAL_NO_LOG ||
mode == RBM_ZERO_ON_ERROR)
pgBufferUsage.local_blks_read++;
}
else
@ -746,7 +749,10 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
strategy, &found);
if (found)
pgBufferUsage.shared_blks_hit++;
else
else if (isExtend)
pgBufferUsage.shared_blks_written++;
else if (mode == RBM_NORMAL || mode == RBM_NORMAL_NO_LOG ||
mode == RBM_ZERO_ON_ERROR)
pgBufferUsage.shared_blks_read++;
}