postgres.git / summary / log / commit / refs

commit    6e466e1e839e2d40b30af9cbda107af867d259f6
Author:   Robert Haas <rhaas@postgresql.org>
Date:     Thu Feb 19 18:46:10 2026 +0000

    Fix add_partial_path interaction with disabled_nodes
    
    Commit e22253467942fdb100087787c3e1e3a8620c54b2 adjusted the logic in
    add_path() to keep the path list sorted by disabled_nodes and then by
    total_cost, but failed to make the corresponding adjustment to
    add_partial_path. As a result, add_partial_path might sort the path list
    just by total cost, which could lead to later planner misbehavior.
    
    In principle, this should be back-patched to v18, but we are typically
    reluctant to back-patch planner fixes for fear of destabilizing working
    installations, and it is unclear to me that this has sufficiently
    serious consequences to justify an exception, so for now, no back-patch.
    
    Reviewed-by: Richard Guo <guofenglinux@gmail.com>
    Discussion: http://postgr.es/m/CAMbWs4-mO3jMK4t_LgcJ+7Eo=NmGgkxettgRaVbJzZvVZ1koMA@mail.gmail.com


 src/backend/optimizer/util/pathnode.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 9678c20ff1f..ef8ef6e89d3 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -758,9 +758,10 @@ add_path_precheck(RelOptInfo *parent_rel, int disabled_nodes,
  *	  parallel such that each worker will generate a subset of the path's
  *	  overall result.
  *
- *	  As in add_path, the partial_pathlist is kept sorted with the cheapest
- *	  total path in front.  This is depended on by multiple places, which
- *	  just take the front entry as the cheapest path without searching.
+ *	  As in add_path, the partial_pathlist is kept sorted first by smallest
+ *    number of disabled nodes and then by lowest total cost. This is depended
+ *    on by multiple places, which just take the front entry as the cheapest
+ *    path without searching.
  *
  *	  We don't generate parameterized partial paths for several reasons.  Most
  *	  importantly, they're not safe to execute, because there's nothing to
@@ -878,8 +879,13 @@ add_partial_path(RelOptInfo *parent_rel, Path *new_path)
 		}
 		else
 		{
-			/* new belongs after this old path if it has cost >= old's */
-			if (new_path->total_cost >= old_path->total_cost)
+			/*
+			 * new belongs after this old path if it has more disabled nodes
+			 * or if it has the same number of nodes but a greater total cost
+			 */
+			if (new_path->disabled_nodes > old_path->disabled_nodes ||
+				(new_path->disabled_nodes == old_path->disabled_nodes &&
+				 new_path->total_cost >= old_path->total_cost))
 				insert_at = foreach_current_index(p1) + 1;
 		}
 


[parent: fc3896c786a2]