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Commitb25dc48

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Fix oversight in sizing of shared buffer lookup hashtable. Because
BufferAlloc tries to insert a new mapping entry before deleting the old onefor a buffer, we have a transient need for more than NBuffers entries ---one more in 8.1, and as many as NUM_BUFFER_PARTITIONS more in CVS HEAD.In theory this could lead to an "out of shared memory" failure if shmemhad already been completely claimed by the time the extra entries wereneeded.
1 parent10b9ca3 commitb25dc48

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‎src/backend/storage/buffer/freelist.c

Lines changed: 11 additions & 4 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
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* $PostgreSQL: pgsql/src/backend/storage/buffer/freelist.c,v 1.55 2006/03/05 15:58:36 momjian Exp $
12+
* $PostgreSQL: pgsql/src/backend/storage/buffer/freelist.c,v 1.56 2006/07/23 18:34:45 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -213,8 +213,8 @@ StrategyShmemSize(void)
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{
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Sizesize=0;
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/* size of lookup hash table */
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size=add_size(size,BufTableShmemSize(NBuffers));
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/* size of lookup hash table... see comment in StrategyInitialize*/
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size=add_size(size,BufTableShmemSize(NBuffers+NUM_BUFFER_PARTITIONS));
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/* size of the shared replacement strategy control block */
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size=add_size(size,MAXALIGN(sizeof(BufferStrategyControl)));
@@ -236,8 +236,15 @@ StrategyInitialize(bool init)
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/*
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* Initialize the shared buffer lookup hashtable.
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*
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* Since we can't tolerate running out of lookup table entries, we
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* must be sure to specify an adequate table size here. The maximum
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* steady-state usage is of course NBuffers entries, but BufferAlloc()
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* tries to insert a new entry before deleting the old. In principle
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* this could be happening in each partition concurrently, so we
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* could need as many as NBuffers + NUM_BUFFER_PARTITIONS entries.
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*/
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InitBufTable(NBuffers);
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InitBufTable(NBuffers+NUM_BUFFER_PARTITIONS);
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/*
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* Get or create the shared strategy control block

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