Change the planner to allow indexscan qualification clauses to use

nonconsecutive columns of a multicolumn index, as per discussion around
mid-May (pghackers thread "Best way to scan on-disk bitmaps").  This
turns out to require only minimal changes in btree, and so far as I can
see none at all in GiST.  btcostestimate did need some work, but its
original assumption that index selectivity == heap selectivity was
quite bogus even before this.

src/backend/access/index/indexam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.82 2005/05/27 23:31:20 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.83 2005/06/13 23:14:48 tgl Exp $
  *
  * INTERFACE ROUTINES
  *		index_open		- open an index relation by relation OID
@@ -25,7 +25,6 @@
  *		index_getmulti	- get multiple tuples from a scan
  *		index_bulk_delete	- bulk deletion of index tuples
  *		index_vacuum_cleanup	- post-deletion cleanup of an index
- *		index_cost_estimator	- fetch amcostestimate procedure OID
  *		index_getprocid - get a support procedure OID
  *		index_getprocinfo - get a support procedure's lookup info
  *
@@ -718,27 +717,6 @@ index_vacuum_cleanup(Relation indexRelation,
 	return result;
 }
 
-/* ----------------
- *		index_cost_estimator
- *
- *		Fetch the amcostestimate procedure OID for an index.
- *
- *		We could combine fetching and calling the procedure,
- *		as index_insert does for example; but that would require
- *		importing a bunch of planner/optimizer stuff into this file.
- * ----------------
- */
-RegProcedure
-index_cost_estimator(Relation indexRelation)
-{
-	FmgrInfo   *procedure;
-
-	RELATION_CHECKS;
-	GET_REL_PROCEDURE(amcostestimate);
-
-	return procedure->fn_oid;
-}
-
 /* ----------------
  *		index_getprocid
  *

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 1.91 2005/03/29 00:16:52 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.92 2005/06/13 23:14:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -594,15 +594,17 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 				}
 
 				/*
-				 * Done if that was the last attribute.
+				 * Done if that was the last attribute, or if next key
+				 * is not in sequence (implying no boundary key is available
+				 * for the next attribute).
 				 */
-				if (i >= so->numberOfKeys)
+				if (i >= so->numberOfKeys ||
+					cur->sk_attno != curattr + 1)
 					break;
 
 				/*
-				 * Reset for next attr, which should be in sequence.
+				 * Reset for next attr.
 				 */
-				Assert(cur->sk_attno == curattr + 1);
 				curattr = cur->sk_attno;
 				chosen = NULL;
 			}

src/backend/access/nbtree/nbtutils.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtutils.c,v 1.62 2004/12/31 21:59:22 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtutils.c,v 1.63 2005/06/13 23:14:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -190,7 +190,9 @@ _bt_formitem(IndexTuple itup)
  * matched to continue the scan.  In general, numberOfRequiredKeys is equal
  * to the number of keys for leading attributes with "=" keys, plus the
  * key(s) for the first non "=" attribute, which can be seen to be correct
- * by considering the above example.
+ * by considering the above example.  Note in particular that if there are no
+ * keys for a given attribute, the keys for subsequent attributes can never
+ * be required; for instance "WHERE y = 4" requires a full-index scan.
  *
  * If possible, redundant keys are eliminated: we keep only the tightest
  * >/>= bound and the tightest </<= bound, and if there's an = key then
@@ -248,8 +250,8 @@ _bt_preprocess_keys(IndexScanDesc scan)
 	outkeys = so->keyData;
 	cur = &inkeys[0];
 	/* we check that input keys are correctly ordered */
-	if (cur->sk_attno != 1)
-		elog(ERROR, "key(s) for attribute 1 missed");
+	if (cur->sk_attno < 1)
+		elog(ERROR, "btree index keys must be ordered by attribute");
 
 	/* We can short-circuit most of the work if there's just one key */
 	if (numberOfKeys == 1)
@@ -270,7 +272,8 @@ _bt_preprocess_keys(IndexScanDesc scan)
 		}
 		memcpy(outkeys, inkeys, sizeof(ScanKeyData));
 		so->numberOfKeys = 1;
-		so->numberOfRequiredKeys = 1;
+		if (cur->sk_attno == 1)
+			so->numberOfRequiredKeys = 1;
 		return;
 	}
 
@@ -324,8 +327,8 @@ _bt_preprocess_keys(IndexScanDesc scan)
 			int			priorNumberOfEqualCols = numberOfEqualCols;
 
 			/* check input keys are correctly ordered */
-			if (i < numberOfKeys && cur->sk_attno != attno + 1)
-				elog(ERROR, "key(s) for attribute %d missed", attno + 1);
+			if (i < numberOfKeys && cur->sk_attno < attno)
+				elog(ERROR, "btree index keys must be ordered by attribute");
 
 			/*
 			 * If = has been specified, no other key will be used. In case