There are some bugs about backward scanning using

indexes.

1. Index Scan using plural indexids never scan backward
   as to the order of indexids.
2. The cursor using Index scan is not usable after moving
   past the end.

This patch solves above bugs.
Moreover the change of _bt_first() would be useful to extend
ORDER BY patch by Jan Wieck for all descending order cases.

Hiroshi Inoue

1 files changed, 34 insertions, 8 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index cdf13c5e19e..16bb4f23b41 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeIndexscan.c,v 1.33 1999/02/21 03:48:40 scrappy Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeIndexscan.c,v 1.34 1999/04/13 17:18:29 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -96,6 +96,8 @@ IndexNext(IndexScan *node)
 	Buffer		buffer = InvalidBuffer;
 	int			numIndices;
 
+ 	bool		bBackward;
+ 	int		indexNumber;
 	/* ----------------
 	 *	extract necessary information from index scan node
 	 * ----------------
@@ -151,8 +153,26 @@ IndexNext(IndexScan *node)
 	 *	appropriate heap tuple.. else return NULL.
 	 * ----------------
 	 */
-	while (indexstate->iss_IndexPtr < numIndices)
-	{
+ 	bBackward = ScanDirectionIsBackward(direction);
+ 	if (bBackward)
+  	{
+ 		indexNumber = numIndices - indexstate->iss_IndexPtr - 1;
+ 		if (indexNumber < 0)
+ 		{
+ 			indexNumber = 0;
+ 			indexstate->iss_IndexPtr = numIndices - 1;
+ 		}
+ 	}
+ 	else
+ 	{
+ 		if ((indexNumber = indexstate->iss_IndexPtr) < 0)
+ 		{
+ 			indexNumber = 0;
+ 			indexstate->iss_IndexPtr = 0;
+ 		}
+ 	}
+ 	while (indexNumber < numIndices)
+ 	{
 		scandesc = scanDescs[indexstate->iss_IndexPtr];
 		while ((result = index_getnext(scandesc, direction)) != NULL)
 		{
@@ -204,8 +224,14 @@ IndexNext(IndexScan *node)
 			if (BufferIsValid(buffer))
 				ReleaseBuffer(buffer);
 		}
-		if (indexstate->iss_IndexPtr < numIndices)
-			indexstate->iss_IndexPtr++;
+ 		if (indexNumber < numIndices)
+ 		{
+ 			indexNumber++;
+ 			if (bBackward)
+ 				indexstate->iss_IndexPtr--;
+ 			else
+ 				indexstate->iss_IndexPtr++;
+ 		}
 	}
 	/* ----------------
 	 *	if we get here it means the index scan failed so we
@@ -294,7 +320,7 @@ ExecIndexReScan(IndexScan *node, ExprContext *exprCtxt, Plan *parent)
 	runtimeKeyInfo = (Pointer *) indexstate->iss_RuntimeKeyInfo;
 	indxqual = node->indxqual;
 	numScanKeys = indexstate->iss_NumScanKeys;
-	indexstate->iss_IndexPtr = 0;
+	indexstate->iss_IndexPtr = -1;
 
 	/* If this is re-scanning of PlanQual ... */
 	if (estate->es_evTuple != NULL && 
@@ -611,7 +637,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate, Plan *parent)
 	  */
 	indexstate = makeNode(IndexScanState);
 	indexstate->iss_NumIndices = 0;
-	indexstate->iss_IndexPtr = 0;
+	indexstate->iss_IndexPtr = -1;
 	indexstate->iss_ScanKeys = NULL;
 	indexstate->iss_NumScanKeys = NULL;
 	indexstate->iss_RuntimeKeyInfo = NULL;
@@ -635,7 +661,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate, Plan *parent)
 	indxid = node->indxid;
 	indxqual = node->indxqual;
 	numIndices = length(indxid);
-	indexPtr = 0;
+	indexPtr = -1;
 
 	CXT1_printf("ExecInitIndexScan: context is %d\n", CurrentMemoryContext);