From d8b04d5fac574d96252230c39a16f651b185661f Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 5 Aug 2008 15:09:04 +0000
Subject: [PATCH] In ReadOrZeroBuffer (and related entry points), don't bother
 to call PageHeaderIsValid when we zero the buffer instead of reading the page
 in. The actual performance improvement is probably marginal since this
 function isn't very heavily used, but a cycle saved is a cycle earned.

Zdenek Kotala
---
 src/backend/storage/buffer/bufmgr.c | 43 +++++++++++++++--------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index e40a815b5d..456dc42336 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.235 2008/08/01 13:16:08 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.236 2008/08/05 15:09:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -352,28 +352,31 @@ ReadBuffer_common(SMgrRelation smgr, bool isLocalBuf, BlockNumber blockNum,
 		if (zeroPage)
 			MemSet((char *) bufBlock, 0, BLCKSZ);
 		else
-			smgrread(smgr, blockNum, (char *) bufBlock);
-		/* check for garbage data */
-		if (!PageHeaderIsValid((PageHeader) bufBlock))
 		{
-			if (zero_damaged_pages)
+			smgrread(smgr, blockNum, (char *) bufBlock);
+
+			/* check for garbage data */
+			if (!PageHeaderIsValid((PageHeader) bufBlock))
 			{
-				ereport(WARNING,
-						(errcode(ERRCODE_DATA_CORRUPTED),
-						 errmsg("invalid page header in block %u of relation %u/%u/%u; zeroing out page",
-								blockNum, 
-								smgr->smgr_rnode.spcNode,
-								smgr->smgr_rnode.dbNode,
-								smgr->smgr_rnode.relNode)));
-				MemSet((char *) bufBlock, 0, BLCKSZ);
+				if (zero_damaged_pages)
+				{
+					ereport(WARNING,
+							(errcode(ERRCODE_DATA_CORRUPTED),
+							 errmsg("invalid page header in block %u of relation %u/%u/%u; zeroing out page",
+									blockNum, 
+									smgr->smgr_rnode.spcNode,
+									smgr->smgr_rnode.dbNode,
+									smgr->smgr_rnode.relNode)));
+					MemSet((char *) bufBlock, 0, BLCKSZ);
+				}
+				else
+					ereport(ERROR,
+							(errcode(ERRCODE_DATA_CORRUPTED),
+							 errmsg("invalid page header in block %u of relation %u/%u/%u",
+									blockNum, smgr->smgr_rnode.spcNode,
+									smgr->smgr_rnode.dbNode,
+									smgr->smgr_rnode.relNode)));
 			}
-			else
-				ereport(ERROR,
-						(errcode(ERRCODE_DATA_CORRUPTED),
-				 errmsg("invalid page header in block %u of relation %u/%u/%u",
-						blockNum, smgr->smgr_rnode.spcNode,
-						smgr->smgr_rnode.dbNode,
-						smgr->smgr_rnode.relNode)));
 		}
 	}
 
-- 
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