From 6f0f98bb0bced134c09b7acf8fe35ff3a6f1bbd2 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 17 Apr 2017 15:29:00 -0400 Subject: [PATCH] Always build a custom plan node's targetlist from the path's pathtarget. We were applying the use_physical_tlist optimization to all relation scan plans, even those implemented by custom scan providers. However, that's a bad idea for a couple of reasons. The custom provider might be unable to provide columns that it hadn't expected to be asked for (for example, the custom scan might depend on an index-only scan). Even more to the point, there's no good reason to suppose that this "optimization" is a win for a custom scan; whatever the custom provider is doing is likely not based on simply returning physical heap tuples. (As a counterexample, if the custom scan is an interface to a column store, demanding all columns would be a huge loss.) If it is a win, the custom provider could make that decision for itself and insert a suitable pathtarget into the path, anyway. Per discussion with Dmitry Ivanov. Back-patch to 9.5 where custom scan support was introduced. The argument that the custom provider can adjust the behavior by changing the pathtarget only applies to 9.6+, but on balance it seems more likely that use_physical_tlist will hurt custom scans than help them. Discussion: https://postgr.es/m/e29ddd30-8ef9-4da5-a50b-2bb7b8c7198d@postgrespro.ru --- src/backend/optimizer/plan/createplan.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c index 6af68b08d27..c464d054c94 100644 --- a/src/backend/optimizer/plan/createplan.c +++ b/src/backend/optimizer/plan/createplan.c @@ -47,7 +47,7 @@ static Plan *create_plan_recurse(PlannerInfo *root, Path *best_path); static Plan *create_scan_plan(PlannerInfo *root, Path *best_path); static List *build_path_tlist(PlannerInfo *root, Path *path); -static bool use_physical_tlist(PlannerInfo *root, RelOptInfo *rel); +static bool use_physical_tlist(PlannerInfo *root, Path *path); static void disuse_physical_tlist(PlannerInfo *root, Plan *plan, Path *path); static Plan *create_gating_plan(PlannerInfo *root, Plan *plan, List *quals); static Plan *create_join_plan(PlannerInfo *root, JoinPath *best_path); @@ -303,7 +303,7 @@ create_scan_plan(PlannerInfo *root, Path *best_path) * planner.c may replace the tlist we generate here, forcing projection to * occur.) */ - if (use_physical_tlist(root, rel)) + if (use_physical_tlist(root, best_path)) { if (best_path->pathtype == T_IndexOnlyScan) { @@ -493,8 +493,9 @@ build_path_tlist(PlannerInfo *root, Path *path) * rather than only those Vars actually referenced. */ static bool -use_physical_tlist(PlannerInfo *root, RelOptInfo *rel) +use_physical_tlist(PlannerInfo *root, Path *path) { + RelOptInfo *rel = path->parent; int i; ListCell *lc; @@ -516,6 +517,13 @@ use_physical_tlist(PlannerInfo *root, RelOptInfo *rel) if (rel->reloptkind != RELOPT_BASEREL) return false; + /* + * Also, don't do it to a CustomPath; the premise that we're extracting + * columns from a simple physical tuple is unlikely to hold for those. + */ + if (IsA(path, CustomPath)) + return false; + /* * Can't do it if any system columns or whole-row Vars are requested. * (This could possibly be fixed but would take some fragile assumptions