From 0fbfd37cefb7eb30c0fa8a158751c19ddeddf1f0 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Tue, 10 Mar 2026 08:33:55 -0400 Subject: [PATCH] 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 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;