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Marginal performance hack: remove the loop that used to be needed to

look through a freelist for a chunk of adequate size. For a long timenow, all elements of a given freelist have been exactly the sameallocated size, so we don't need a loop. Since the loop never iteratedmore than once, you'd think this wouldn't matter much, but it makes anoticeable savings in a simple test --- perhaps because the compilerisn't optimizing on a mistaken assumption that the loop would repeat.AllocSetAlloc is called often enough that saving even a couple ofinstructions is worthwhile.

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src/backend/utils/mmgr
- aset.c

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-18

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`‎src/backend/utils/mmgr/aset.c`

Lines changed: 7 additions & 18 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 1.71 2007/01/05 22:19:47 momjian Exp $`
	`14`	`+ * $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.72 2007/04/30 00:12:08 tgl Exp $`
`15`	`15`	`*`
`16`	`16`	`* NOTE:`
`17`	`17`	`*This is a new (Feb. 05, 1999) implementation of the allocation set`
`@@ -516,7 +516,6 @@ AllocSetAlloc(MemoryContext context, Size size)`
`516`	`516`	`AllocSetset= (AllocSet)context;`
`517`	`517`	`AllocBlockblock;`
`518`	`518`	`AllocChunkchunk;`
`519`		`-AllocChunkpriorfree;`
`520`	`519`	`intfidx;`
`521`	`520`	`Sizechunk_size;`
`522`	`521`	`Sizeblksize;`
`@@ -578,26 +577,16 @@ AllocSetAlloc(MemoryContext context, Size size)`
`578`	`577`	`/*`
`579`	`578`	`* Request is small enough to be treated as a chunk. Look in the`
`580`	`579`	`* corresponding free list to see if there is a free chunk we could reuse.`
`581`		`- */`
`582`		`-fidx=AllocSetFreeIndex(size);`
`583`		`-priorfree=NULL;`
`584`		`-for (chunk=set->freelist[fidx];chunk;chunk= (AllocChunk)chunk->aset)`
`585`		`-{`
`586`		`-if (chunk->size >=size)`
`587`		`-break;`
`588`		`-priorfree=chunk;`
`589`		`-}`
`590`		`-`
`591`		`-/*`
`592`	`580`	`* If one is found, remove it from the free list, make it again a member`
`593`	`581`	`* of the alloc set and return its data address.`
`594`	`582`	`*/`
	`583`	`+fidx=AllocSetFreeIndex(size);`
	`584`	`+chunk=set->freelist[fidx];`
`595`	`585`	`if (chunk!=NULL)`
`596`	`586`	`{`
`597`		`-if (priorfree==NULL)`
`598`		`-set->freelist[fidx]= (AllocChunk)chunk->aset;`
`599`		`-else`
`600`		`-priorfree->aset=chunk->aset;`
	`587`	`+Assert(chunk->size >=size);`
	`588`	`+`
	`589`	`+set->freelist[fidx]= (AllocChunk)chunk->aset;`
`601`	`590`
`602`	`591`	`chunk->aset= (void*)set;`
`603`	`592`
`@@ -618,7 +607,7 @@ AllocSetAlloc(MemoryContext context, Size size)`
`618`	`607`	`/*`
`619`	`608`	`* Choose the actual chunk size to allocate.`
`620`	`609`	`*/`
`621`		`-chunk_size=1 <<(fidx+ALLOC_MINBITS);`
	`610`	`+chunk_size=(1 <<ALLOC_MINBITS) <<fidx;`
`622`	`611`	`Assert(chunk_size >=size);`
`623`	`612`
`624`	`613`	`/*`

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`‎src/backend/utils/mmgr/aset.c`

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