postgrespro.git / summary / log / commit / refs

commit    d67dae036bd71afd2be7a2fafd7bc1ef38bfcdd1
Author:   Thomas Munro <tmunro@postgresql.org>
Date:     Tue Nov 27 22:42:32 2018 +0000

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


 src/backend/storage/buffer/bufmgr.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 01eabe5706..9817770aff 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -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++;
 	}
 


[parent: 471a7af585b1]