From 1f542a2eacca030c676cbb594f3b362d43f2f857 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 13 Dec 2016 13:20:16 -0500 Subject: [PATCH] Prevent planagg.c from failing on queries containing CTEs. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The existing tests in preprocess_minmax_aggregates() usually prevent it from trying to do anything with queries containing CTEs, but there's an exception: a CTE could be present as a member of an appendrel, if we flattened a UNION ALL that contains CTE references. If it did try to generate an optimized path for a query using a CTE, it failed with "could not find plan for CTE", as reported by Torsten Förtsch. The proximate cause is an unwise decision in commit 3fc6e2d7f to clear subroot->cte_plan_ids in build_minmax_path(). That left the subroot's cte_plan_ids list out of step with its parse->cteList. Removing the "subroot->cte_plan_ids = NIL;" assignment is enough to let the case work again, but really it's pretty silly to be expending any cycles at all in this module when there are CTEs: we always treat their outputs as unordered so there's no way for the optimization to win. Hence, also add an early-exit test so we don't waste time like that. Back-patch to 9.6 where the misbehavior was introduced. Report: https://postgr.es/m/CAKkG4_=gjY5QiHtqSZyWMwDuTd_CftKoTaCqxjJ7uUz1-Gw=qw@mail.gmail.com --- src/backend/optimizer/plan/planagg.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/src/backend/optimizer/plan/planagg.c b/src/backend/optimizer/plan/planagg.c index 805aae7ee7..4216fc4a6e 100644 --- a/src/backend/optimizer/plan/planagg.c +++ b/src/backend/optimizer/plan/planagg.c @@ -103,6 +103,14 @@ preprocess_minmax_aggregates(PlannerInfo *root, List *tlist) parse->hasWindowFuncs) return; + /* + * Reject if query contains any CTEs; there's no way to build an indexscan + * on one so we couldn't succeed here. (If the CTEs are unreferenced, + * that's not true, but it doesn't seem worth expending cycles to check.) + */ + if (parse->cteList) + return; + /* * We also restrict the query to reference exactly one table, since join * conditions can't be handled reasonably. (We could perhaps handle a @@ -360,7 +368,6 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo, subroot->plan_params = NIL; subroot->outer_params = NULL; subroot->init_plans = NIL; - subroot->cte_plan_ids = NIL; subroot->parse = parse = (Query *) copyObject(root->parse); IncrementVarSublevelsUp((Node *) parse, 1, 1); -- 2.40.0