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Improve realloc() per idea from Karel Zak --- if chunk to be enlarged is

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at end of its block, maybe we can enlarge it in-place.
This commit is contained in:
Tom Lane 2001-01-23 01:01:36 +00:00
parent c0bb21b369
commit 728b0aa290
1 changed files with 52 additions and 2 deletions
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54
src/backend/utils/mmgr/aset.c
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@ -11,7 +11,7 @@
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.37 2001/01/12 21:54:01 tgl Exp $ * $Header: /cvsroot/pgsql/src/backend/utils/mmgr/aset.c,v 1.38 2001/01/23 01:01:36 tgl Exp $
* *
* NOTE: * NOTE:
* This is a new (Feb. 05, 1999) implementation of the allocation set * This is a new (Feb. 05, 1999) implementation of the allocation set
@ -879,10 +879,60 @@ AllocSetRealloc(MemoryContext context, void *pointer, Size size)
} }
else else
{ {
/*
* Small-chunk case. If the chunk is the last one in its block,
* there might be enough free space after it that we can just
* enlarge the chunk in-place. It's relatively painful to find
* the containing block in the general case, but we can detect
* last-ness quite cheaply for the typical case where the chunk
* is in the active (topmost) allocation block. (At least with
* the regression tests and code as of 1/2001, realloc'ing the last
* chunk of a non-topmost block hardly ever happens, so it's not
* worth scanning the block list to catch that case.)
*
* NOTE: must be careful not to create a chunk of a size that
* AllocSetAlloc would not create, else we'll get confused later.
*/
AllocPointer newPointer;
if (size <= ALLOC_CHUNK_LIMIT)
{
AllocBlock block = set->blocks;
char *chunk_end;
chunk_end = (char *) chunk + (oldsize + ALLOC_CHUNKHDRSZ);
if (chunk_end == block->freeptr)
{
/* OK, it's last in block ... is there room? */
Size freespace = block->endptr - block->freeptr;
int fidx;
Size newsize;
Size delta;
fidx = AllocSetFreeIndex(size);
newsize = 1 << (fidx + ALLOC_MINBITS);
Assert(newsize >= oldsize);
delta = newsize - oldsize;
if (freespace >= delta)
{
/* Yes, so just enlarge the chunk. */
block->freeptr += delta;
chunk->size += delta;
#ifdef MEMORY_CONTEXT_CHECKING
chunk->requested_size = size;
/* set mark to catch clobber of "unused" space */
if (size < chunk->size)
((char *) pointer)[size] = 0x7E;
#endif
return pointer;
}
}
}
/* Normal small-chunk case: just do it by brute force. */ /* Normal small-chunk case: just do it by brute force. */
/* allocate new chunk */ /* allocate new chunk */
AllocPointer newPointer = AllocSetAlloc((MemoryContext) set, size); newPointer = AllocSetAlloc((MemoryContext) set, size);
/* transfer existing data (certain to fit) */ /* transfer existing data (certain to fit) */
memcpy(newPointer, pointer, oldsize); memcpy(newPointer, pointer, oldsize);