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Commit72619f8

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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 memorymanagement overhead when num_temp_buffers is large: in the previous codingwe would actually waste 50% of the space used for temp buffers, because aset.cwould round the individual requests up to 16K. Problem noted while studyinga performance issue reported by Steven Flatt.Back-patch as far as 8.1 --- older versions used few enough local buffersthat the issue isn't significant for them.
1 parentc22dea8 commit72619f8

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+51
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1 file changed

+51
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‎src/backend/storage/buffer/localbuf.c‎

Lines changed: 51 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@
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*
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*
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* IDENTIFICATION
12-
* $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.74 2006/03/31 23:32:06 tgl Exp $
12+
* $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.75 2006/12/27 22:31:54 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -48,6 +48,7 @@ static HTAB *LocalBufHash = NULL;
4848

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5050
staticvoidInitLocalBuffers(void);
51+
staticBlockGetLocalBufferStorage(void);
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/*
@@ -167,12 +168,8 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
167168
*/
168169
if (LocalBufHdrGetBlock(bufHdr)==NULL)
169170
{
170-
char*data;
171-
172-
data= (char*)MemoryContextAlloc(TopMemoryContext,BLCKSZ);
173-
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/* Set pointer for use by BufferGetBlock() macro */
175-
LocalBufHdrGetBlock(bufHdr)=(Block)data;
172+
LocalBufHdrGetBlock(bufHdr)=GetLocalBufferStorage();
176173
}
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178175
/*
@@ -334,6 +331,54 @@ InitLocalBuffers(void)
334331
NLocBuffer=nbufs;
335332
}
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334+
/*
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* GetLocalBufferStorage - allocate memory for a local buffer
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*
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* The idea of this function is to aggregate our requests for storage
338+
* so that the memory manager doesn't see a whole lot of relatively small
339+
* requests. Since we'll never give back a local buffer once it's created
340+
* within a particular process, no point in burdening memmgr with separately
341+
* managed chunks.
342+
*/
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staticBlock
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GetLocalBufferStorage(void)
345+
{
346+
staticchar*cur_block=NULL;
347+
staticintnext_buf_in_block=0;
348+
staticintnum_bufs_in_block=0;
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staticinttotal_bufs_allocated=0;
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351+
char*this_buf;
352+
353+
Assert(total_bufs_allocated<NLocBuffer);
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355+
if (next_buf_in_block >=num_bufs_in_block)
356+
{
357+
/* Need to make a new request to memmgr */
358+
intnum_bufs;
359+
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/* Start with a 16-buffer request; subsequent ones double each time */
361+
num_bufs=Max(num_bufs_in_block*2,16);
362+
/* But not more than what we need for all remaining local bufs */
363+
num_bufs=Min(num_bufs,NLocBuffer-total_bufs_allocated);
364+
/* And don't overflow MaxAllocSize, either */
365+
num_bufs=Min(num_bufs,MaxAllocSize /BLCKSZ);
366+
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/* Allocate space from TopMemoryContext so it never goes away */
368+
cur_block= (char*)MemoryContextAlloc(TopMemoryContext,
369+
num_bufs*BLCKSZ);
370+
next_buf_in_block=0;
371+
num_bufs_in_block=num_bufs;
372+
}
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374+
/* Allocate next buffer in current memory block */
375+
this_buf=cur_block+next_buf_in_block*BLCKSZ;
376+
next_buf_in_block++;
377+
total_bufs_allocated++;
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379+
return (Block)this_buf;
380+
}
381+
337382
/*
338383
* AtEOXact_LocalBuffers - clean up at end of transaction.
339384
*

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