From a3699c599ced03ace09646b74b8299d8f570ca76 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 30 Jul 2022 13:05:15 -0400 Subject: [PATCH] Fix incorrect is-this-the-topmost-join tests in parallel planning. Two callers of generate_useful_gather_paths were testing the wrong thing when deciding whether to call that function: they checked for being at the top of the current join subproblem, rather than being at the actual top join. This'd result in failing to construct parallel paths for a sub-join for which they might be useful. While set_rel_pathlist() isn't actively broken, it seems best to make its identical-in-intention test for this be like the other two. This has been wrong all along, but given the lack of field complaints I'm hesitant to back-patch into stable branches; we usually prefer to avoid non-bug-fix changes in plan choices in minor releases. It seems not too late for v15 though. Richard Guo, reviewed by Antonin Houska and Tom Lane Discussion: https://postgr.es/m/CAMbWs4-mH8Zf87-w+3P2J=nJB+5OyicO28ia9q_9o=Lamf_VHg@mail.gmail.com --- src/backend/optimizer/geqo/geqo_eval.c | 2 +- src/backend/optimizer/path/allpaths.c | 9 ++++----- 2 files changed, 5 insertions(+), 6 deletions(-) diff --git a/src/backend/optimizer/geqo/geqo_eval.c b/src/backend/optimizer/geqo/geqo_eval.c index de695c0a78..004481d608 100644 --- a/src/backend/optimizer/geqo/geqo_eval.c +++ b/src/backend/optimizer/geqo/geqo_eval.c @@ -273,7 +273,7 @@ merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, int num_gene, * rel once we know the final targetlist (see * grouping_planner). */ - if (old_clump->size + new_clump->size < num_gene) + if (!bms_equal(joinrel->relids, root->all_baserels)) generate_useful_gather_paths(root, joinrel, false); /* Find and save the cheapest paths for this joinrel */ diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index e9342097e5..4cf0cdc4be 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -553,12 +553,11 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, * its own pool of workers. Instead, we'll consider gathering partial * paths for the parent appendrel. * - * Also, if this is the topmost scan/join rel (that is, the only baserel), - * we postpone gathering until the final scan/join targetlist is available - * (see grouping_planner). + * Also, if this is the topmost scan/join rel, we postpone gathering until + * the final scan/join targetlist is available (see grouping_planner). */ if (rel->reloptkind == RELOPT_BASEREL && - bms_membership(root->all_baserels) != BMS_SINGLETON) + !bms_equal(rel->relids, root->all_baserels)) generate_useful_gather_paths(root, rel, false); /* Now find the cheapest of the paths for this rel */ @@ -3402,7 +3401,7 @@ standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels) * partial paths. We'll do the same for the topmost scan/join rel * once we know the final targetlist (see grouping_planner). */ - if (lev < levels_needed) + if (!bms_equal(rel->relids, root->all_baserels)) generate_useful_gather_paths(root, rel, false); /* Find and save the cheapest paths for this rel */