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Modify local buffer management to request memory for local buffers in blocks 

of increasing size, instead of one at a time.  This reduces the memory
management overhead when num_temp_buffers is large: in the previous coding
we would actually waste 50% of the space used for temp buffers, because aset.c
would round the individual requests up to 16K.  Problem noted while studying
a performance issue reported by Steven Flatt.

Back-patch as far as 8.1 --- older versions used few enough local buffers
that the issue isn't significant for them.
This commit is contained in:
Tom Lane 2006-12-27 22:31:54 +00:00
parent c22dea8900
commit 72619f8191
1 changed files with 51 additions and 6 deletions
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57
src/backend/storage/buffer/localbuf.c
View File

@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.74 2006/03/31 23:32:06 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.75 2006/12/27 22:31:54 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -48,6 +48,7 @@ static HTAB *LocalBufHash = NULL;
static void InitLocalBuffers(void);
static Block GetLocalBufferStorage(void);
/*
@ -167,12 +168,8 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
*/
if (LocalBufHdrGetBlock(bufHdr) == NULL)
{
char *data;
data = (char *) MemoryContextAlloc(TopMemoryContext, BLCKSZ);
/* Set pointer for use by BufferGetBlock() macro */
LocalBufHdrGetBlock(bufHdr) = (Block) data;
LocalBufHdrGetBlock(bufHdr) = GetLocalBufferStorage();
}
/*
@ -334,6 +331,54 @@ InitLocalBuffers(void)
NLocBuffer = nbufs;
}
/*
* GetLocalBufferStorage - allocate memory for a local buffer
*
* The idea of this function is to aggregate our requests for storage
* so that the memory manager doesn't see a whole lot of relatively small
* requests. Since we'll never give back a local buffer once it's created
* within a particular process, no point in burdening memmgr with separately
* managed chunks.
*/
static Block
GetLocalBufferStorage(void)
{
static char *cur_block = NULL;
static int next_buf_in_block = 0;
static int num_bufs_in_block = 0;
static int total_bufs_allocated = 0;
char *this_buf;
Assert(total_bufs_allocated < NLocBuffer);
if (next_buf_in_block >= num_bufs_in_block)
{
/* Need to make a new request to memmgr */
int num_bufs;
/* Start with a 16-buffer request; subsequent ones double each time */
num_bufs = Max(num_bufs_in_block * 2, 16);
/* But not more than what we need for all remaining local bufs */
num_bufs = Min(num_bufs, NLocBuffer - total_bufs_allocated);
/* And don't overflow MaxAllocSize, either */
num_bufs = Min(num_bufs, MaxAllocSize / BLCKSZ);
/* Allocate space from TopMemoryContext so it never goes away */
cur_block = (char *) MemoryContextAlloc(TopMemoryContext,
num_bufs * BLCKSZ);
next_buf_in_block = 0;
num_bufs_in_block = num_bufs;
}
/* Allocate next buffer in current memory block */
this_buf = cur_block + next_buf_in_block * BLCKSZ;
next_buf_in_block++;
total_bufs_allocated++;
return (Block) this_buf;
}
/*
* AtEOXact_LocalBuffers - clean up at end of transaction.
*