Avoid unnecessary palloc overhead in _bt_first(). The temporary

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 ...

diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index 824d5ea70e66b51b232d50f0358012c9832d399c..42bd6574aafb84b1ddd75200f81c57e6441e391b 100644 (file)
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -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