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Avoid unnecessary palloc overhead in _bt_first(). The temporary

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scankeys arrays that it needs can never have more than INDEX_MAX_KEYS
entries, so it's reasonable to just allocate them as fixed-size local
arrays, and save the cost of palloc/pfree.  Not a huge savings, but
a cycle saved is a cycle earned ...
This commit is contained in:
Tom Lane 2005-06-19 22:41:00 +00:00
parent fc654583ab
commit d961a56899
1 changed files with 4 additions and 21 deletions
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25
src/backend/access/nbtree/nbtsearch.c
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@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.92 2005/06/13 23:14:48 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.93 2005/06/19 22:41:00 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -495,8 +495,8 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
bool nextkey;
bool goback;
bool continuescan;
ScanKey scankeys;
ScanKey *startKeys = NULL;
ScanKey startKeys[INDEX_MAX_KEYS];
ScanKeyData scankeys[INDEX_MAX_KEYS];
int keysCount = 0;
int i;
StrategyNumber strat_total;
@ -552,8 +552,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
ScanKey chosen;
ScanKey cur;
startKeys = (ScanKey *) palloc(so->numberOfKeys * sizeof(ScanKey));
/*
* chosen is the so-far-chosen key for the current attribute, if
* any. We don't cast the decision in stone until we reach keys
@ -636,18 +634,14 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* scan from there.
*/
if (keysCount == 0)
{
if (startKeys)
pfree(startKeys);
return _bt_endpoint(scan, dir);
}
/*
* We want to start the scan somewhere within the index. Set up a
* 3-way-comparison scankey we can use to search for the boundary
* point we identified above.
*/
scankeys = (ScanKey) palloc(keysCount * sizeof(ScanKeyData));
Assert(keysCount <= INDEX_MAX_KEYS);
for (i = 0; i < keysCount; i++)
{
ScanKey cur = startKeys[i];
@ -657,12 +651,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* code later
*/
if (cur->sk_flags & SK_ISNULL)
{
pfree(startKeys);
pfree(scankeys);
elog(ERROR, "btree doesn't support is(not)null, yet");
return false;
}
/*
* If scankey operator is of default subtype, we can use the
@ -699,8 +688,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
}
}
pfree(startKeys);
/*
* Examine the selected initial-positioning strategy to determine
* exactly where we need to start the scan, and set flag variables to
@ -809,7 +796,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
/* Only get here if index is completely empty */
ItemPointerSetInvalid(current);
so->btso_curbuf = InvalidBuffer;
pfree(scankeys);
return false;
}
@ -823,9 +809,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
blkno = BufferGetBlockNumber(buf);
ItemPointerSet(current, blkno, offnum);
/* done with manufactured scankey, now */
pfree(scankeys);
/*
* If nextkey = false, we are positioned at the first item >= scan
* key, or possibly at the end of a page on which all the existing