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Remove BufferBlockPointers array in favor of a base + (bufnum) * BLCKSZ 

computation.  On modern machines this is as fast if not faster, and we
don't have to clog the CPU's L2 cache with a tens-of-KB pointer array.
If we ever decide to adopt a more dynamic allocation method for shared
buffers, we'll probably have to revert this patch, but in the meantime
we might as well save a few bytes and nanoseconds.  Per Qingqing Zhou.
This commit is contained in:
Tom Lane 2005-08-12 05:05:51 +00:00
parent b609695b7a
commit 3ae7e4a33b
3 changed files with 7 additions and 28 deletions
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25
src/backend/storage/buffer/buf_init.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_init.c,v 1.74 2005/08/08 03:11:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_init.c,v 1.75 2005/08/12 05:05:50 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -19,11 +19,9 @@
BufferDesc *BufferDescriptors;
Block *BufferBlockPointers;
char *BufferBlocks;
int32 *PrivateRefCount;
static char *BufferBlocks;
/* statistics counters */
long int ReadBufferCount;
long int ReadLocalBufferCount;
@ -154,30 +152,11 @@ InitBufferPool(void)
void
InitBufferPoolAccess(void)
{
char *block;
int i;
/*
* Allocate and zero local arrays of per-buffer info.
*/
BufferBlockPointers = (Block *) calloc(NBuffers,
sizeof(*BufferBlockPointers));
PrivateRefCount = (int32 *) calloc(NBuffers,
sizeof(*PrivateRefCount));
/*
* Construct addresses for the individual buffer data blocks. We do
* this just to speed up the BufferGetBlock() macro. (Since the
* addresses should be the same in every backend, we could inherit
* this data from the postmaster --- but in the EXEC_BACKEND case
* that doesn't work.)
*/
block = BufferBlocks;
for (i = 0; i < NBuffers; i++)
{
BufferBlockPointers[i] = (Block) block;
block += BLCKSZ;
}
}
/*

4
src/backend/storage/buffer/bufmgr.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.192 2005/08/08 19:44:22 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.193 2005/08/12 05:05:50 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -54,7 +54,7 @@
/* Note: these two macros only work on shared buffers, not local ones! */
#define BufHdrGetBlock(bufHdr) BufferBlockPointers[(bufHdr)->buf_id]
#define BufHdrGetBlock(bufHdr) ((Block) (BufferBlocks + ((Size) (bufHdr)->buf_id) * BLCKSZ))
#define BufferGetLSN(bufHdr) (*((XLogRecPtr*) BufHdrGetBlock(bufHdr)))
/* Note: this macro only works on local buffers, not shared ones! */

6
src/include/storage/bufmgr.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.94 2005/08/08 03:12:16 tgl Exp $
* $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.95 2005/08/12 05:05:51 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -33,7 +33,7 @@ extern int bgwriter_lru_maxpages;
extern int bgwriter_all_maxpages;
/* in buf_init.c */
extern DLLIMPORT Block *BufferBlockPointers;
extern DLLIMPORT char *BufferBlocks;
extern DLLIMPORT int32 *PrivateRefCount;
/* in localbuf.c */
@ -107,7 +107,7 @@ extern DLLIMPORT int32 *LocalRefCount;
BufferIsLocal(buffer) ? \
LocalBufferBlockPointers[-(buffer) - 1] \
: \
BufferBlockPointers[(buffer) - 1] \
(Block) (BufferBlocks + ((Size) ((buffer) - 1)) * BLCKSZ) \
)
/*