[HACKERS] small improvement in buffread common

[Zdenek Kotala]

I attach patch which removes useless page header check when page is zeroed. It 
is primary used by hash index.

        Zdenek
--
Zdenek Kotala              Sun Microsystems
Prague, Czech Republic     http://sun.com/postgresql

*** pgsql_page_api.7c9eff0cf439/src/backend/storage/buffer/bufmgr.c	út srp  5 12:31:44 2008
--- pgsql_page_api/src/backend/storage/buffer/bufmgr.c	út srp  5 12:25:01 2008
***************
*** 352,379 ****
  		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)
  			{
! 				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)));
  		}
  	}
  
--- 352,382 ----
  		if (zeroPage)
  			MemSet((char *) bufBlock, 0, BLCKSZ);
  		else
  		{
! 			smgrread(smgr, blockNum, (char *) bufBlock);
! 
! 			/* check for garbage data */
! 			if (!PageHeaderIsValid((Page) bufBlock))
  			{
! 				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)));
  			}
  		}
  	}
  
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