From 0ea5eee37606386150aa8317184617e1d5d34565 Mon Sep 17 00:00:00 2001 From: Richard Guo Date: Wed, 5 Nov 2025 18:10:54 +0900 Subject: [PATCH] Avoid creating duplicate ordered append paths In generate_orderedappend_paths(), the function does not handle the case where the paths in total_subpaths and fractional_subpaths are identical. This situation is not uncommon, and as a result, it may generate two exactly identical ordered append paths. Fix by checking whether total_subpaths and fractional_subpaths contain the same paths, and skipping creation of the ordered append path for the fractional case when they are identical. Given the lack of field complaints about this, I'm a bit hesitant to back-patch, but let's clean it up in HEAD. Author: Richard Guo Reviewed-by: Andrei Lepikhov Reviewed-by: Alexander Korotkov Discussion: https://postgr.es/m/CAMbWs4-OYsgA75tGGiBARt87G0y_z_GBTSLrzudcJxAzndYkYw@mail.gmail.com --- src/backend/optimizer/path/allpaths.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index 41233b98373..4c43fd0b19b 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -1877,6 +1877,7 @@ generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, List *total_subpaths = NIL; List *fractional_subpaths = NIL; bool startup_neq_total = false; + bool fraction_neq_total = false; bool match_partition_order; bool match_partition_order_desc; int end_index; @@ -2005,15 +2006,21 @@ generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, * XXX We might consider partially sorted paths too (with an * incremental sort on top). But we'd have to build all the * incremental paths, do the costing etc. + * + * Also, notice whether we actually have different paths for + * the "fractional" and "total" cases. This helps avoid + * generating two identical ordered append paths. */ - if (!cheapest_fractional) + if (cheapest_fractional == NULL) cheapest_fractional = cheapest_total; + else if (cheapest_fractional != cheapest_total) + fraction_neq_total = true; } /* * Notice whether we actually have different paths for the - * "cheapest" and "total" cases; frequently there will be no point - * in two create_merge_append_path() calls. + * "cheapest" and "total" cases. This helps avoid generating two + * identical ordered append paths. */ if (cheapest_startup != cheapest_total) startup_neq_total = true; @@ -2084,7 +2091,7 @@ generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, false, -1)); - if (fractional_subpaths) + if (fractional_subpaths && fraction_neq_total) add_path(rel, (Path *) create_append_path(root, rel, fractional_subpaths, @@ -2110,7 +2117,7 @@ generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel, pathkeys, NULL)); - if (fractional_subpaths) + if (fractional_subpaths && fraction_neq_total) add_path(rel, (Path *) create_merge_append_path(root, rel, fractional_subpaths, -- 2.47.3