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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

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`‎src/backend/utils/mmgr/aset.c`

Lines changed: 4 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -11,7 +11,7 @@`
`11`	`11`	`* Portions Copyright (c) 1994, Regents of the University of California`
`12`	`12`	`*`
`13`	`13`	`* IDENTIFICATION`
`14`		`- * $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.54 2003/11/29 19:52:04 pgsql Exp $`
	`14`	`+ * $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.55 2004/05/26 19:44:15 tgl Exp $`
`15`	`15`	`*`
`16`	`16`	`* NOTE:`
`17`	`17`	`*This is a new (Feb. 05, 1999) implementation of the allocation set`
`@@ -85,16 +85,16 @@`
`85`	`85`	`* CAUTION: ALLOC_MINBITS must be large enough so that`
`86`	`86`	`* 1<<ALLOC_MINBITS is at least MAXALIGN,`
`87`	`87`	`* or we may fail to align the smallest chunks adequately.`
`88`		`- *16-byte alignment is enough on all currently known machines.`
	`88`	`+ *8-byte alignment is enough on all currently known machines.`
`89`	`89`	`*`
`90`	`90`	`* With the current parameters, request sizes up to 8K are treated as chunks,`
`91`	`91`	`* larger requests go into dedicated blocks. Change ALLOCSET_NUM_FREELISTS`
`92`	`92`	`* to adjust the boundary point.`
`93`	`93`	`*--------------------`
`94`	`94`	`*/`
`95`	`95`
`96`		`-#defineALLOC_MINBITS4/* smallest chunk size is16 bytes */`
`97`		`-#defineALLOCSET_NUM_FREELISTS10`
	`96`	`+#defineALLOC_MINBITS3/* smallest chunk size is8 bytes */`
	`97`	`+#defineALLOCSET_NUM_FREELISTS11`
`98`	`98`	`#defineALLOC_CHUNK_LIMIT(1 << (ALLOCSET_NUM_FREELISTS-1+ALLOC_MINBITS))`
`99`	`99`	`/* Size of largest chunk that we use a fixed size for */`
`100`	`100`

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Commit4646a8f

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`‎src/backend/utils/mmgr/aset.c`

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