Support "x IS NOT NULL" clauses as indexscan conditions. This turns out

to be just a minor extension of the previous patch that made "x IS NULL"
indexable, because we can treat the IS NOT NULL condition as if it were
"x < NULL" or "x > NULL" (depending on the index's NULLS FIRST/LAST option),
just like IS NULL is treated like "x = NULL".  Aside from any possible
usefulness in its own right, this is an important improvement for
index-optimized MAX/MIN aggregates: it is now reliably possible to get
a column's min or max value cheaply, even when there are a lot of nulls
cluttering the interesting end of the index.

1 files changed, 14 insertions, 8 deletions

diff --git a/src/backend/access/gist/gistget.c b/src/backend/access/gist/gistget.c
index a094495b8a..98104a7a9f 100644
--- a/src/backend/access/gist/gistget.c
+++ b/src/backend/access/gist/gistget.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gistget.c,v 1.82 2009/10/08 22:34:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistget.c,v 1.83 2010/01/01 21:53:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -413,14 +413,20 @@ gistindex_keytest(IndexTuple tuple,
 		{
 			/*
 			 * On non-leaf page we can't conclude that child hasn't NULL
-			 * values because of assumption in GiST: uinon (VAL, NULL) is VAL
-			 * But if on non-leaf page key IS  NULL then all childs has NULL.
+			 * values because of assumption in GiST: union (VAL, NULL) is VAL.
+			 * But if on non-leaf page key IS NULL, then all children are NULL.
 			 */
-
-			Assert(key->sk_flags & SK_SEARCHNULL);
-
-			if (GistPageIsLeaf(p) && !isNull)
-				return false;
+			if (key->sk_flags & SK_SEARCHNULL)
+			{
+				if (GistPageIsLeaf(p) && !isNull)
+					return false;
+			}
+			else
+			{
+				Assert(key->sk_flags & SK_SEARCHNOTNULL);
+				if (isNull)
+					return false;
+			}
 		}
 		else if (isNull)
 		{