Push index operator lossiness determination down to GIST/GIN opclass

"consistent" functions, and remove pg_amop.opreqcheck, as per recent
discussion.  The main immediate benefit of this is that we no longer need
8.3's ugly hack of requiring @@@ rather than @@ to test weight-using tsquery
searches on GIN indexes.  In future it should be possible to optimize some
other queries better than is done now, by detecting at runtime whether the
index match is exact or not.

Tom Lane, after an idea of Heikki's, and with some help from Teodor.

1 files changed, 22 insertions, 11 deletions

diff --git a/src/backend/access/gist/gistget.c b/src/backend/access/gist/gistget.c
index 8e92139582..7a5177218e 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 1.71 2008/04/13 19:18:14 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistget.c,v 1.72 2008/04/14 17:05:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -151,7 +151,6 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 	GISTScanOpaque so;
 	GISTSearchStack *stk;
 	IndexTuple	it;
-	bool		recheck;
 	GISTPageOpaque opaque;
 	bool		resetoffset = false;
 	int64		ntids = 0;
@@ -257,8 +256,6 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 		for (;;)
 		{
 			n = gistfindnext(scan, n, dir);
-			/* XXX for the moment, treat all GIST operators as lossy */
-			recheck = true;
 
 			if (!OffsetNumberIsValid(n))
 			{
@@ -304,11 +301,11 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 					it = (IndexTuple) PageGetItem(p, PageGetItemId(p, n));
 					ntids++;
 					if (tbm != NULL)
-						tbm_add_tuples(tbm, &it->t_tid, 1, recheck);
+						tbm_add_tuples(tbm, &it->t_tid, 1, scan->xs_recheck);
 					else 
 					{
 						scan->xs_ctup.t_self = it->t_tid;
-						scan->xs_recheck = recheck;
+						/* scan->xs_recheck is already set */
 
 						LockBuffer(so->curbuf, GIST_UNLOCK);
 						return ntids; /* always 1 */
@@ -345,6 +342,10 @@ gistnext(IndexScanDesc scan, ScanDirection dir, TIDBitmap *tbm)
 /*
  * gistindex_keytest() -- does this index tuple satisfy the scan key(s)?
  *
+ * On success return for a leaf tuple, scan->xs_recheck is set to indicate
+ * whether recheck is needed.  We recheck if any of the consistent() functions
+ * request it.
+ *
  * We must decompress the key in the IndexTuple before passing it to the
  * sk_func (and we have previously overwritten the sk_func to use the
  * user-defined Consistent method, so we actually are invoking that).
@@ -371,6 +372,8 @@ gistindex_keytest(IndexTuple tuple,
 
 	IncrIndexProcessed();
 
+	scan->xs_recheck = false;
+
 	/*
 	 * Tuple doesn't restore after crash recovery because of incomplete insert
 	 */
@@ -382,6 +385,7 @@ gistindex_keytest(IndexTuple tuple,
 		Datum		datum;
 		bool		isNull;
 		Datum		test;
+		bool		recheck;
 		GISTENTRY	de;
 
 		datum = index_getattr(tuple,
@@ -408,7 +412,6 @@ gistindex_keytest(IndexTuple tuple,
 		}
 		else
 		{
-
 			gistdentryinit(giststate, key->sk_attno - 1, &de,
 						   datum, r, p, offset,
 						   FALSE, isNull);
@@ -416,21 +419,28 @@ gistindex_keytest(IndexTuple tuple,
 			/*
 			 * Call the Consistent function to evaluate the test.  The
 			 * arguments are the index datum (as a GISTENTRY*), the comparison
-			 * datum, and the comparison operator's strategy number and
-			 * subtype from pg_amop.
+			 * datum, the comparison operator's strategy number and
+			 * subtype from pg_amop, and the recheck flag.
 			 *
 			 * (Presently there's no need to pass the subtype since it'll
 			 * always be zero, but might as well pass it for possible future
 			 * use.)
+			 *
+			 * We initialize the recheck flag to true (the safest assumption)
+			 * in case the Consistent function forgets to set it.
 			 */
-			test = FunctionCall4(&key->sk_func,
+			recheck = true;
+
+			test = FunctionCall5(&key->sk_func,
 								 PointerGetDatum(&de),
 								 key->sk_argument,
 								 Int32GetDatum(key->sk_strategy),
-								 ObjectIdGetDatum(key->sk_subtype));
+								 ObjectIdGetDatum(key->sk_subtype),
+								 PointerGetDatum(&recheck));
 
 			if (!DatumGetBool(test))
 				return false;
+			scan->xs_recheck |= recheck;
 		}
 
 		keySize--;
@@ -444,6 +454,7 @@ gistindex_keytest(IndexTuple tuple,
  * Return the offset of the first index entry that is consistent with
  * the search key after offset 'n' in the current page. If there are
  * no more consistent entries, return InvalidOffsetNumber.
+ * On success, scan->xs_recheck is set correctly, too.
  * Page should be locked....
  */
 static OffsetNumber