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Commit4646a8f

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Reduce the minimum allocable chunk size to 8 bytes (from 16). Now that
ListCells are only 8 bytes instead of 12 (on 4-byte-pointer machinesanyway), it's worth maintaining a separate freelist for 8-byte objects.Remembering that alloc chunks carry 8 bytes of overhead, this shouldreduce the net storage requirement for a long List by about a third.
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‎src/backend/utils/mmgr/aset.c‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.54 2003/11/29 19:52:04 pgsql Exp $
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* $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.55 2004/05/26 19:44:15 tgl Exp $
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*
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* NOTE:
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*This is a new (Feb. 05, 1999) implementation of the allocation set
@@ -85,16 +85,16 @@
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* CAUTION: ALLOC_MINBITS must be large enough so that
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* 1<<ALLOC_MINBITS is at least MAXALIGN,
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* or we may fail to align the smallest chunks adequately.
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*16-byte alignment is enough on all currently known machines.
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*8-byte alignment is enough on all currently known machines.
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*
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* With the current parameters, request sizes up to 8K are treated as chunks,
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* larger requests go into dedicated blocks. Change ALLOCSET_NUM_FREELISTS
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* to adjust the boundary point.
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*--------------------
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*/
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#defineALLOC_MINBITS4/* smallest chunk size is16 bytes */
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#defineALLOCSET_NUM_FREELISTS10
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#defineALLOC_MINBITS3/* smallest chunk size is8 bytes */
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#defineALLOCSET_NUM_FREELISTS11
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#defineALLOC_CHUNK_LIMIT(1 << (ALLOCSET_NUM_FREELISTS-1+ALLOC_MINBITS))
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/* Size of largest chunk that we use a fixed size for */
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