postgres.git / summary / log / commit / refs

commit    0fbfd37cefb7eb30c0fa8a158751c19ddeddf1f0
Author:   Robert Haas <rhaas@postgresql.org>
Date:     Tue Mar 10 12:33:55 2026 +0000

    Allow extensions to mark an individual index as disabled.
    
    Up until now, the only way for a loadable module to disable the use of a
    particular index was to use build_simple_rel_hook (or, previous to
    yesterday's commit, get_relation_info_hook) to remove it from the index
    list. While that works, it has some disadvantages. First, the index
    becomes invisible for all purposes, and can no longer be used for
    optimizations such as self-join elimination or left join removal, which
    can severely degrade the resulting plan.
    
    Second, if the module attempts to compel the use of a certain index
    by removing all other indexes from the index list and disabling
    other scan types, but the planner is unable to use the chosen index
    for some reason, it will fall back to a sequential scan, because that
    is only disabled, whereas the other indexes are, from the planner's
    point of view, completely gone. While this situation ideally shouldn't
    occur, it's hard for a loadable module to be completely sure whether
    the planner will view a certain index as usable for a certain query.
    If it isn't, it may be better to fall back to a scan using a disabled
    index rather than falling back to an also-disabled sequential scan.
    
    Reviewed-by: Alexandra Wang <alexandra.wang.oss@gmail.com>
    Discussion: http://postgr.es/m/CA%2BTgmoYS4ZCVAF2jTce%3DbMP0Oq_db_srocR4cZyO0OBp9oUoGg%40mail.gmail.com


 src/backend/optimizer/util/pathnode.c | 8 ++++++++
 src/include/nodes/pathnodes.h         | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index c94e077000f..96cc72a776b 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1122,6 +1122,14 @@ create_index_path(PlannerInfo *root,
 
 	cost_index(pathnode, root, loop_count, partial_path);
 
+	/*
+	 * cost_index will set disabled_nodes to 1 if this rel is not allowed to
+	 * use index scans in general, but it doesn't have the IndexOptInfo to
+	 * know whether this specific index has been disabled.
+	 */
+	if (index->disabled)
+		pathnode->path.disabled_nodes = 1;
+
 	return pathnode;
 }
 
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index c175ee95b68..27758ec16fe 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -1412,6 +1412,8 @@ typedef struct IndexOptInfo
 	bool		nullsnotdistinct;
 	/* is uniqueness enforced immediately? */
 	bool		immediate;
+	/* true if paths using this index should be marked disabled */
+	bool		disabled;
 	/* true if index doesn't really exist */
 	bool		hypothetical;
 


[parent: 03facc1211b0]