From 1baba95ea4d800de7d9ffcd24f04cec279cde518 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Sun, 28 Jul 2019 15:59:05 +0200 Subject: [PATCH 5/8] Consider incremental sort paths in additional places --- src/backend/optimizer/path/allpaths.c | 221 +++++++++++++++++++++++++- src/backend/optimizer/plan/planner.c | 130 ++++++++++++++- src/include/optimizer/paths.h | 2 + 3 files changed, 350 insertions(+), 3 deletions(-) diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index ccf46dd0aa..9a92948fe3 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -556,7 +556,7 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, */ if (rel->reloptkind == RELOPT_BASEREL && bms_membership(root->all_baserels) != BMS_SINGLETON) - generate_gather_paths(root, rel, false); + generate_useful_gather_paths(root, rel, false); /* Now find the cheapest of the paths for this rel */ set_cheapest(rel); @@ -2727,6 +2727,223 @@ generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows) } } +/* + * Find an equivalence class member expression, all of whose Vars, come from + * the indicated relation. + */ +static Expr * +find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel) +{ + ListCell *lc_em; + + foreach(lc_em, ec->ec_members) + { + EquivalenceMember *em = lfirst(lc_em); + + if (bms_is_subset(em->em_relids, rel->relids) && + !bms_is_empty(em->em_relids)) + { + /* + * If there is more than one equivalence member whose Vars are + * taken entirely from this relation, we'll be content to choose + * any one of those. + */ + return em->em_expr; + } + } + + /* We didn't find any suitable equivalence class expression */ + return NULL; +} + +/* + * get_useful_pathkeys_for_relation + * Determine which orderings of a relation might be useful. + * + * Getting data in sorted order can be useful either because the requested + * order matches the final output ordering for the overall query we're + * planning, or because it enables an efficient merge join. Here, we try + * to figure out which pathkeys to consider. + */ +static List * +get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel) +{ + List *useful_pathkeys_list = NIL; + ListCell *lc; + + /* + * Pushing the query_pathkeys to the remote server is always worth + * considering, because it might let us avoid a local sort. + */ + if (root->query_pathkeys) + { + bool query_pathkeys_ok = true; + + foreach(lc, root->query_pathkeys) + { + PathKey *pathkey = (PathKey *) lfirst(lc); + EquivalenceClass *pathkey_ec = pathkey->pk_eclass; + Expr *em_expr; + + /* + * The planner and executor don't have any clever strategy for + * taking data sorted by a prefix of the query's pathkeys and + * getting it to be sorted by all of those pathkeys. We'll just + * end up re-sorting the entire data set. So, unless we can push + * down all of the query pathkeys, forget it. + * + * is_foreign_expr would detect volatile expressions as well, but + * checking ec_has_volatile here saves some cycles. + */ + if (pathkey_ec->ec_has_volatile || + !(em_expr = find_em_expr_for_rel(pathkey_ec, rel))) + { + query_pathkeys_ok = false; + break; + } + } + + /* + * This ends up allowing us to do incremental sort on top of an index + * scan all parallelized under a gather merge node. + */ + if (query_pathkeys_ok) + useful_pathkeys_list = list_make1(list_copy(root->query_pathkeys)); + } + + return useful_pathkeys_list; +} + +/* + * generate_useful_gather_paths + * Generate parallel access paths for a relation by pushing a Gather or + * Gather Merge on top of a partial path. + * + * Unlike generate_gather_paths, this does not look only at pathkeys of the + * input paths (aiming to preserve the ordering). It also considers ordering + * that might be useful by nodes above the gather merge node, and tries to + * add a sort (regular or incremental) to provide that. + */ +void +generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows) +{ + ListCell *lc; + double rows; + double *rowsp = NULL; + List *useful_pathkeys_list = NIL; + Path *cheapest_partial_path = NULL; + + /* If there are no partial paths, there's nothing to do here. */ + if (rel->partial_pathlist == NIL) + return; + + /* Should we override the rel's rowcount estimate? */ + if (override_rows) + rowsp = &rows; + + /* generate the regular gather merge paths */ + generate_gather_paths(root, rel, override_rows); + + /* when incremental sort is disabled, we're done */ + if (!enable_incrementalsort) + return; + + /* consider incremental sort for interesting orderings */ + useful_pathkeys_list = get_useful_pathkeys_for_relation(root, rel); + + /* used for explicit sort paths */ + cheapest_partial_path = linitial(rel->partial_pathlist); + + /* + * Consider incremental sort paths for each interesting ordering. + * + * XXX I wonder if we need to consider adding a projection here, as + * create_ordered_paths does. + */ + foreach(lc, useful_pathkeys_list) + { + List *useful_pathkeys = lfirst(lc); + ListCell *lc2; + bool is_sorted; + int presorted_keys; + + foreach(lc2, rel->partial_pathlist) + { + Path *subpath = (Path *) lfirst(lc2); + GatherMergePath *path; + + /* path has no ordering at all, can't use incremental sort */ + if (subpath->pathkeys == NIL) + continue; + + is_sorted = pathkeys_common_contained_in(useful_pathkeys, + subpath->pathkeys, + &presorted_keys); + + if (is_sorted) + { + path = create_gather_merge_path(root, rel, subpath, rel->reltarget, + subpath->pathkeys, NULL, rowsp); + + add_path(rel, &path->path); + continue; + } + + Assert(!is_sorted); + + /* + * consider regular sort for cheapest partial path (for each + * useful pathkeys) + */ + if (cheapest_partial_path == subpath) + { + Path *tmp; + + tmp = (Path *) create_sort_path(root, + rel, + subpath, + useful_pathkeys, + -1.0); + + rows = tmp->rows * tmp->parallel_workers; + + path = create_gather_merge_path(root, rel, + tmp, + rel->reltarget, + tmp->pathkeys, + NULL, + rowsp); + + add_path(rel, &path->path); + + /* Fall through */ + } + + /* Also consider incremental sort */ + if (presorted_keys > 0) + { + Path *tmp; + + tmp = (Path *) create_incremental_sort_path(root, + rel, + subpath, + useful_pathkeys, + presorted_keys, + -1); + + path = create_gather_merge_path(root, rel, + tmp, + rel->reltarget, + tmp->pathkeys, + NULL, + rowsp); + + add_path(rel, &path->path); + } + } + } +} + /* * make_rel_from_joinlist * Build access paths using a "joinlist" to guide the join path search. @@ -2899,7 +3116,7 @@ standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels) * once we know the final targetlist (see grouping_planner). */ if (lev < levels_needed) - generate_gather_paths(root, rel, false); + generate_useful_gather_paths(root, rel, false); /* Find and save the cheapest paths for this rel */ set_cheapest(rel); diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index 0e01cf8cb1..46dc355af3 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -6434,7 +6434,9 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel, foreach(lc, input_rel->pathlist) { Path *path = (Path *) lfirst(lc); + Path *path_original = path; bool is_sorted; + int presorted_keys; is_sorted = pathkeys_contained_in(root->group_pathkeys, path->pathkeys); @@ -6493,6 +6495,80 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel, Assert(false); } } + + /* + * Now we may consider incremental sort on this path, but only + * when the path is not already sorted and when incremental sort + * is enabled. + */ + if (is_sorted || !enable_incrementalsort) + continue; + + /* Restore the input path (we might have added Sort on top). */ + path = path_original; + + is_sorted = pathkeys_common_contained_in(root->group_pathkeys, + path->pathkeys, + &presorted_keys); + + /* We've already skipped fully sorted paths above. */ + Assert(!is_sorted); + + /* no shared prefix, not point in building incremental sort */ + if (presorted_keys == 0) + continue; + + path = (Path *) create_incremental_sort_path(root, + grouped_rel, + path, + root->group_pathkeys, + presorted_keys, + -1.0); + + /* Now decide what to stick atop it */ + if (parse->groupingSets) + { + consider_groupingsets_paths(root, grouped_rel, + path, true, can_hash, + gd, agg_costs, dNumGroups); + } + else if (parse->hasAggs) + { + /* + * We have aggregation, possibly with plain GROUP BY. Make + * an AggPath. + */ + add_path(grouped_rel, (Path *) + create_agg_path(root, + grouped_rel, + path, + grouped_rel->reltarget, + parse->groupClause ? AGG_SORTED : AGG_PLAIN, + AGGSPLIT_SIMPLE, + parse->groupClause, + havingQual, + agg_costs, + dNumGroups)); + } + else if (parse->groupClause) + { + /* + * We have GROUP BY without aggregation or grouping sets. + * Make a GroupPath. + */ + add_path(grouped_rel, (Path *) + create_group_path(root, + grouped_rel, + path, + parse->groupClause, + havingQual, + dNumGroups)); + } + else + { + /* Other cases should have been handled above */ + Assert(false); + } } /* @@ -6819,7 +6895,9 @@ create_partial_grouping_paths(PlannerInfo *root, foreach(lc, input_rel->partial_pathlist) { Path *path = (Path *) lfirst(lc); + Path *path_original = path; bool is_sorted; + int presorted_keys; is_sorted = pathkeys_contained_in(root->group_pathkeys, path->pathkeys); @@ -6854,6 +6932,56 @@ create_partial_grouping_paths(PlannerInfo *root, NIL, dNumPartialPartialGroups)); } + + /* + * Now we may consider incremental sort on this path, but only + * when the path is not already sorted and when incremental sort + * is enabled. + */ + if (is_sorted || !enable_incrementalsort) + continue; + + /* Restore the input path (we might have added Sort on top). */ + path = path_original; + + is_sorted = pathkeys_common_contained_in(root->group_pathkeys, + path->pathkeys, + &presorted_keys); + + /* We've already skipped fully sorted paths above. */ + Assert(!is_sorted); + + /* no shared prefix, not point in building incremental sort */ + if (presorted_keys == 0) + continue; + + path = (Path *) create_incremental_sort_path(root, + partially_grouped_rel, + path, + root->group_pathkeys, + presorted_keys, + -1.0); + + if (parse->hasAggs) + add_partial_path(partially_grouped_rel, (Path *) + create_agg_path(root, + partially_grouped_rel, + path, + partially_grouped_rel->reltarget, + parse->groupClause ? AGG_SORTED : AGG_PLAIN, + AGGSPLIT_INITIAL_SERIAL, + parse->groupClause, + NIL, + agg_partial_costs, + dNumPartialPartialGroups)); + else + add_partial_path(partially_grouped_rel, (Path *) + create_group_path(root, + partially_grouped_rel, + path, + parse->groupClause, + NIL, + dNumPartialPartialGroups)); } } @@ -7235,7 +7363,7 @@ apply_scanjoin_target_to_paths(PlannerInfo *root, * one of the generated paths may turn out to be the cheapest one. */ if (rel->consider_parallel && !IS_OTHER_REL(rel)) - generate_gather_paths(root, rel, false); + generate_useful_gather_paths(root, rel, false); /* * Reassess which paths are the cheapest, now that we've potentially added diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h index 85f5fe37ea..f6994779de 100644 --- a/src/include/optimizer/paths.h +++ b/src/include/optimizer/paths.h @@ -54,6 +54,8 @@ extern RelOptInfo *standard_join_search(PlannerInfo *root, int levels_needed, extern void generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows); +extern void generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, + bool override_rows); extern int compute_parallel_worker(RelOptInfo *rel, double heap_pages, double index_pages, int max_workers); extern void create_partial_bitmap_paths(PlannerInfo *root, RelOptInfo *rel, -- 2.21.1