Phase 2 of project to make index operator lossiness be determined at runtime

instead of plan time.  Extend the amgettuple API so that the index AM returns
a boolean indicating whether the indexquals need to be rechecked, and make
that rechecking happen in nodeIndexscan.c (currently the only place where
it's expected to be needed; other callers of index_getnext are just erroring
out for now).  For the moment, GIN and GIST have stub logic that just always
sets the recheck flag to TRUE --- I'm hoping to get Teodor to handle pushing
that control down to the opclass consistent() functions.  The planner no
longer pays any attention to amopreqcheck, and that catalog column will go
away in due course.

1 files changed, 14 insertions, 2 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index 59f54ee5cb4..7b6e3df6506 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.126 2008/03/18 03:54:52 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.127 2008/04/13 19:18:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -106,7 +106,7 @@ IndexNext(IndexScanState *node)
 	/*
 	 * ok, now that we have what we need, fetch the next tuple.
 	 */
-	if ((tuple = index_getnext(scandesc, direction)) != NULL)
+	while ((tuple = index_getnext(scandesc, direction)) != NULL)
 	{
 		/*
 		 * Store the scanned tuple in the scan tuple slot of the scan state.
@@ -118,6 +118,18 @@ IndexNext(IndexScanState *node)
 					   scandesc->xs_cbuf,		/* buffer containing tuple */
 					   false);	/* don't pfree */
 
+		/*
+		 * If the index was lossy, we have to recheck the index quals using
+		 * the real tuple.
+		 */
+		if (scandesc->xs_recheck)
+		{
+			econtext->ecxt_scantuple = slot;
+			ResetExprContext(econtext);
+			if (!ExecQual(node->indexqualorig, econtext, false))
+				continue;		/* nope, so ask index for another one */
+		}
+
 		return slot;
 	}