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commit    39a0db101105eab3f4044d11c609c58b9459ea16
Author:   David Rowley <drowley@postgresql.org>
Date:     Wed Sep 23 13:20:02 2026 +0000

    Fix incorrect block accounting in TID Range Scans
    
    heapgettup_advance_block() (or heapgettup() and heapgettup_pagemode() in
    versions before v16) would incorrectly decrement rs_numblocks when
    advancing to the next block.  Ordinarily this was fine, but if the TID
    Range scan plan was used by a scrollable cursor and the cursor was fetched
    backwards enough to result in another block being required, then
    rs_numblocks may have reached 0 prematurely resulting in the scan ending
    prematurely.
    
    Reported-by: Jeff Davis <pgsql@j-davis.com>
    Author: Ewan Young <kdbase.hack@gmail.com>
    Author: David Rowley <dgrowleyml@gmail.com>
    Discussion: https://postgr.es/m/6b50233fcc0f7d6f4845f083777fa9702d9612e4.camel@j-davis.com
    Backpatch-through: 14


 src/backend/access/heap/heapam.c           | 20 +++++++++++---------
 src/test/regress/expected/tidrangescan.out | 26 ++++++++++++++++++++++++++
 src/test/regress/sql/tidrangescan.sql      | 12 ++++++++++++
 3 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index d72b41ef92f..9ee86340bdc 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -847,7 +847,11 @@ heapgettup_advance_block(HeapScanDesc scan, BlockNumber block, ScanDirection dir
 		/* check if the limit imposed by heap_setscanlimits() is met */
 		if (scan->rs_numblocks != InvalidBlockNumber)
 		{
-			if (--scan->rs_numblocks == 0)
+			BlockNumber endblock;
+
+			endblock = (scan->rs_startblock + scan->rs_numblocks) %
+				scan->rs_nblocks;
+			if (block == endblock)
 				return InvalidBlockNumber;
 		}
 
@@ -855,17 +859,15 @@ heapgettup_advance_block(HeapScanDesc scan, BlockNumber block, ScanDirection dir
 	}
 	else
 	{
-		/* we're done if the last block is the start position */
+		/*
+		 * We're done if the last block is the start position.  No need to
+		 * check if rs_numblocks was set by heap_setscanlimits() as that only
+		 * changes the end block.  The start block is the same with or without
+		 * scan limits.
+		 */
 		if (block == scan->rs_startblock)
 			return InvalidBlockNumber;
 
-		/* check if the limit imposed by heap_setscanlimits() is met */
-		if (scan->rs_numblocks != InvalidBlockNumber)
-		{
-			if (--scan->rs_numblocks == 0)
-				return InvalidBlockNumber;
-		}
-
 		/* wrap to the end of the heap when the last page was page 0 */
 		if (block == 0)
 			block = scan->rs_nblocks;
diff --git a/src/test/regress/expected/tidrangescan.out b/src/test/regress/expected/tidrangescan.out
index 721f3b94e04..3ccef0fd0c2 100644
--- a/src/test/regress/expected/tidrangescan.out
+++ b/src/test/regress/expected/tidrangescan.out
@@ -295,6 +295,32 @@ FETCH LAST c;
  (0,10)
 (1 row)
 
+COMMIT;
+-- Ensure TID Range Scans with scrollable cursors count blocks correctly.
+BEGIN;
+DECLARE c SCROLL CURSOR FOR SELECT ctid FROM tidrangescan WHERE ctid >= '(0,1)' AND ctid <= '(2,10)';
+MOVE FORWARD 25 c;
+MOVE BACKWARD 4 c;
+FETCH BACKWARD 1 c;
+  ctid  
+--------
+ (1,10)
+(1 row)
+
+MOVE BACKWARD ALL c;
+FETCH FORWARD 1 c;
+ ctid  
+-------
+ (0,1)
+(1 row)
+
+MOVE FORWARD ALL c;
+FETCH BACKWARD 1 c;
+  ctid  
+--------
+ (2,10)
+(1 row)
+
 COMMIT;
 DROP TABLE tidrangescan;
 RESET enable_seqscan;
diff --git a/src/test/regress/sql/tidrangescan.sql b/src/test/regress/sql/tidrangescan.sql
index ac09ebb6262..e367292e885 100644
--- a/src/test/regress/sql/tidrangescan.sql
+++ b/src/test/regress/sql/tidrangescan.sql
@@ -96,6 +96,18 @@ FETCH FIRST c;
 FETCH LAST c;
 COMMIT;
 
+-- Ensure TID Range Scans with scrollable cursors count blocks correctly.
+BEGIN;
+DECLARE c SCROLL CURSOR FOR SELECT ctid FROM tidrangescan WHERE ctid >= '(0,1)' AND ctid <= '(2,10)';
+MOVE FORWARD 25 c;
+MOVE BACKWARD 4 c;
+FETCH BACKWARD 1 c;
+MOVE BACKWARD ALL c;
+FETCH FORWARD 1 c;
+MOVE FORWARD ALL c;
+FETCH BACKWARD 1 c;
+COMMIT;
+
 DROP TABLE tidrangescan;
 
 RESET enable_seqscan;


[parent: 71672056784f]