From 714aacfea72dfa202457923befefa3a401309369 Mon Sep 17 00:00:00 2001 From: jcoleman Date: Sun, 29 Nov 2020 09:13:02 -0500 Subject: [PATCH v3 5/5] Document find_em_expr_usable_for_sorting_rel in prepare_sort_from_pathkeys --- src/backend/optimizer/path/equivclass.c | 9 ++++++--- src/backend/optimizer/plan/createplan.c | 3 +++ 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c index e098b6066b..067c969100 100644 --- a/src/backend/optimizer/path/equivclass.c +++ b/src/backend/optimizer/path/equivclass.c @@ -798,9 +798,12 @@ find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel) } /* - * Find an equivalence class member expression that can be safely used by a - * sort node on top of the provided relation. The rules here must match those - * applied in prepare_sort_from_pathkeys. + * Find an equivalence class member expression that can be safely used to build + * a sort node using the provided relation. The applied rules parallel those + * applied in prepare_sort_from_pathkeys but are a subset of that function since + * here we are concerned with proactive sorts while prepare_sort_from_pathkeys + * must deal with sorts that must be delayed until the last stages of query + * execution. */ Expr * find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel, bool require_parallel_safe) diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c index 40abe6f9f6..db31ee6c0f 100644 --- a/src/backend/optimizer/plan/createplan.c +++ b/src/backend/optimizer/plan/createplan.c @@ -5848,6 +5848,9 @@ make_incrementalsort(Plan *lefttree, int numCols, int nPresortedCols, * * Returns the node which is to be the input to the Sort (either lefttree, * or a Result stacked atop lefttree). + * + * Note: Restrictions on what expressions are safely sortable may also need to + * be added to find_em_expr_usable_for_sorting_rel. */ static Plan * prepare_sort_from_pathkeys(Plan *lefttree, List *pathkeys, -- 2.17.1