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Avoid unnecessary palloc overhead in _bt_first(). The temporary

scankeys arrays that it needs can never have more than INDEX_MAX_KEYSentries, so it's reasonable to just allocate them as fixed-size localarrays, and save the cost of palloc/pfree. Not a huge savings, buta cycle saved is a cycle earned ...

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src/backend/access/nbtree
- nbtsearch.c

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-21

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`‎src/backend/access/nbtree/nbtsearch.c‎`

Lines changed: 4 additions & 21 deletions

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`* Portions Copyright (c) 1994, Regents of the University of California`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.92 2005/06/13 23:14:48 tgl Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.93 2005/06/19 22:41:00 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*-------------------------------------------------------------------------`
`14`	`14`	`*/`
`@@ -495,8 +495,8 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`495`	`495`	`boolnextkey;`
`496`	`496`	`boolgoback;`
`497`	`497`	`boolcontinuescan;`
`498`		`-ScanKeyscankeys;`
`499`		`-ScanKey*startKeys=NULL;`
	`498`	`+ScanKeystartKeys[INDEX_MAX_KEYS];`
	`499`	`+ScanKeyDatascankeys[INDEX_MAX_KEYS];`
`500`	`500`	`intkeysCount=0;`
`501`	`501`	`inti;`
`502`	`502`	`StrategyNumberstrat_total;`
`@@ -552,8 +552,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`552`	`552`	`ScanKeychosen;`
`553`	`553`	`ScanKeycur;`
`554`	`554`
`555`		`-startKeys= (ScanKey)palloc(so->numberOfKeyssizeof(ScanKey));`
`556`		`-`
`557`	`555`	`/*`
`558`	`556`	`* chosen is the so-far-chosen key for the current attribute, if`
`559`	`557`	`* any. We don't cast the decision in stone until we reach keys`
`@@ -636,18 +634,14 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`636`	`634`	`* scan from there.`
`637`	`635`	`*/`
`638`	`636`	`if (keysCount==0)`
`639`		`-{`
`640`		`-if (startKeys)`
`641`		`-pfree(startKeys);`
`642`	`637`	`return_bt_endpoint(scan,dir);`
`643`		`-}`
`644`	`638`
`645`	`639`	`/*`
`646`	`640`	`* We want to start the scan somewhere within the index. Set up a`
`647`	`641`	`* 3-way-comparison scankey we can use to search for the boundary`
`648`	`642`	`* point we identified above.`
`649`	`643`	`*/`
`650`		`-scankeys= (ScanKey)palloc(keysCount*sizeof(ScanKeyData));`
	`644`	`+Assert(keysCount<=INDEX_MAX_KEYS);`
`651`	`645`	`for (i=0;i<keysCount;i++)`
`652`	`646`	`{`
`653`	`647`	`ScanKeycur=startKeys[i];`
`@@ -657,12 +651,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`657`	`651`	`* code later`
`658`	`652`	`*/`
`659`	`653`	`if (cur->sk_flags&SK_ISNULL)`
`660`		`-{`
`661`		`-pfree(startKeys);`
`662`		`-pfree(scankeys);`
`663`	`654`	`elog(ERROR,"btree doesn't support is(not)null, yet");`
`664`		`-return false;`
`665`		`-}`
`666`	`655`
`667`	`656`	`/*`
`668`	`657`	`* If scankey operator is of default subtype, we can use the`
`@@ -699,8 +688,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`699`	`688`	`}`
`700`	`689`	`}`
`701`	`690`
`702`		`-pfree(startKeys);`
`703`		`-`
`704`	`691`	`/*`
`705`	`692`	`* Examine the selected initial-positioning strategy to determine`
`706`	`693`	`* exactly where we need to start the scan, and set flag variables to`
`@@ -809,7 +796,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`809`	`796`	`/* Only get here if index is completely empty */`
`810`	`797`	`ItemPointerSetInvalid(current);`
`811`	`798`	`so->btso_curbuf=InvalidBuffer;`
`812`		`-pfree(scankeys);`
`813`	`799`	`return false;`
`814`	`800`	`}`
`815`	`801`
`@@ -823,9 +809,6 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)`
`823`	`809`	`blkno=BufferGetBlockNumber(buf);`
`824`	`810`	`ItemPointerSet(current,blkno,offnum);`
`825`	`811`
`826`		`-/* done with manufactured scankey, now */`
`827`		`-pfree(scankeys);`
`828`		`-`
`829`	`812`	`/*`
`830`	`813`	`* If nextkey = false, we are positioned at the first item >= scan`
`831`	`814`	`* key, or possibly at the end of a page on which all the existing`

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`‎src/backend/access/nbtree/nbtsearch.c‎`

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