Buy back some of the cycles spent in more-expensive hash functions by

selecting power-of-2, rather than prime, numbers of buckets in hash joins.
If the hash functions are doing their jobs properly by making all hash bits
equally random, this is good enough, and it saves expensive integer division
and modulus operations.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/include/executor/hashjoin.h b/src/include/executor/hashjoin.h
index 19cfb1c473b..8056cd88e92 100644
--- a/src/include/executor/hashjoin.h
+++ b/src/include/executor/hashjoin.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/hashjoin.h,v 1.44 2007/01/30 01:33:36 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/executor/hashjoin.h,v 1.45 2007/06/01 17:38:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -76,6 +76,8 @@ typedef struct HashJoinTupleData
 typedef struct HashJoinTableData
 {
 	int			nbuckets;		/* # buckets in the in-memory hash table */
+	int			log2_nbuckets;	/* its log2 (nbuckets must be a power of 2) */
+
 	/* buckets[i] is head of list of tuples in i'th in-memory bucket */
 	struct HashJoinTupleData **buckets;
 	/* buckets array is per-batch storage, as are all the tuples */