From a3179ab692be4314d5ee5cd56598976c487d5ef2 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 27 Sep 2024 16:04:04 -0400 Subject: [PATCH] Recalculate where-needed data accurately after a join removal. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Up to now, remove_rel_from_query() has done a pretty shoddy job of updating our where-needed bitmaps (per-Var attr_needed and per-PlaceHolderVar ph_needed relid sets). It removed direct mentions of the to-be-removed baserel and outer join, which is the minimum amount of effort needed to keep the data structures self-consistent. But it didn't account for the fact that the removed join ON clause probably mentioned Vars of other relations, and those Vars might now not be needed as high up in the join tree as before. It's easy to show cases where this results in failing to remove a lower outer join that could also have been removed. To fix, recalculate the where-needed bitmaps from scratch after each successful join removal. This sounds expensive, but it seems to add only negligible planner runtime. (We cheat a little bit by preserving "relation 0" entries in the bitmaps, allowing us to skip re-scanning the targetlist and HAVING qual.) The submitted test case drew attention because we had successfully optimized away the lower join prior to v16. I suspect that that's somewhat accidental and there are related cases that were never optimized before and now can be. I've not tried to come up with one, though. Perhaps we should back-patch this into v16 and v17 to repair the performance regression. However, since it took a year for anyone to notice the problem, it can't be affecting too many people. Let's let the patch bake awhile in HEAD, and see if we get more complaints. Per bug #18627 from Mikaël Gourlaouen. No back-patch for now. Discussion: https://postgr.es/m/18627-44f950eb6a8416c2@postgresql.org --- src/backend/optimizer/path/equivclass.c | 41 ++++- src/backend/optimizer/plan/analyzejoins.c | 85 ++++++---- src/backend/optimizer/plan/initsplan.c | 179 +++++++++++++++++++++- src/backend/optimizer/util/placeholder.c | 27 ++++ src/include/optimizer/paths.h | 1 + src/include/optimizer/placeholder.h | 1 + src/include/optimizer/planmain.h | 4 + src/test/regress/expected/join.out | 12 +- src/test/regress/sql/join.sql | 7 +- 9 files changed, 320 insertions(+), 37 deletions(-) diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c index 47644b26c6a..8f6f005ecb9 100644 --- a/src/backend/optimizer/path/equivclass.c +++ b/src/backend/optimizer/path/equivclass.c @@ -1293,7 +1293,8 @@ generate_base_implied_equalities_no_const(PlannerInfo *root, * For the moment we force all the Vars to be available at all join nodes * for this eclass. Perhaps this could be improved by doing some * pre-analysis of which members we prefer to join, but it's no worse than - * what happened in the pre-8.3 code. + * what happened in the pre-8.3 code. (Note: rebuild_eclass_attr_needed + * needs to match this code.) */ foreach(lc, ec->ec_members) { @@ -2422,6 +2423,44 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo) return false; /* failed to make any deduction */ } +/* + * rebuild_eclass_attr_needed + * Put back attr_needed bits for Vars/PHVs needed for join eclasses. + * + * This is used to rebuild attr_needed/ph_needed sets after removal of a + * useless outer join. It should match what + * generate_base_implied_equalities_no_const did, except that we call + * add_vars_to_attr_needed not add_vars_to_targetlist. + */ +void +rebuild_eclass_attr_needed(PlannerInfo *root) +{ + ListCell *lc; + + foreach(lc, root->eq_classes) + { + EquivalenceClass *ec = (EquivalenceClass *) lfirst(lc); + + /* Need do anything only for a multi-member, no-const EC. */ + if (list_length(ec->ec_members) > 1 && !ec->ec_has_const) + { + ListCell *lc2; + + foreach(lc2, ec->ec_members) + { + EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2); + List *vars = pull_var_clause((Node *) cur_em->em_expr, + PVC_RECURSE_AGGREGATES | + PVC_RECURSE_WINDOWFUNCS | + PVC_INCLUDE_PLACEHOLDERS); + + add_vars_to_attr_needed(root, vars, ec->ec_relids); + list_free(vars); + } + } + } +} + /* * find_join_domain * Find the highest JoinDomain enclosed within the given relid set. diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c index c3fd4a81f8a..928d926645e 100644 --- a/src/backend/optimizer/plan/analyzejoins.c +++ b/src/backend/optimizer/plan/analyzejoins.c @@ -27,6 +27,7 @@ #include "optimizer/optimizer.h" #include "optimizer/pathnode.h" #include "optimizer/paths.h" +#include "optimizer/placeholder.h" #include "optimizer/planmain.h" #include "optimizer/restrictinfo.h" #include "utils/lsyscache.h" @@ -341,35 +342,6 @@ remove_rel_from_query(PlannerInfo *root, int relid, SpecialJoinInfo *sjinfo) Assert(ojrelid != 0); joinrelids = bms_add_member(joinrelids, ojrelid); - /* - * Remove references to the rel from other baserels' attr_needed arrays. - */ - for (rti = 1; rti < root->simple_rel_array_size; rti++) - { - RelOptInfo *otherrel = root->simple_rel_array[rti]; - int attroff; - - /* there may be empty slots corresponding to non-baserel RTEs */ - if (otherrel == NULL) - continue; - - Assert(otherrel->relid == rti); /* sanity check on array */ - - /* no point in processing target rel itself */ - if (otherrel == rel) - continue; - - for (attroff = otherrel->max_attr - otherrel->min_attr; - attroff >= 0; - attroff--) - { - otherrel->attr_needed[attroff] = - bms_del_member(otherrel->attr_needed[attroff], relid); - otherrel->attr_needed[attroff] = - bms_del_member(otherrel->attr_needed[attroff], ojrelid); - } - } - /* * Update all_baserels and related relid sets. */ @@ -450,9 +422,11 @@ remove_rel_from_query(PlannerInfo *root, int relid, SpecialJoinInfo *sjinfo) phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, relid); phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, ojrelid); Assert(!bms_is_empty(phinfo->ph_eval_at)); /* checked previously */ - phinfo->ph_needed = bms_del_member(phinfo->ph_needed, relid); - phinfo->ph_needed = bms_del_member(phinfo->ph_needed, ojrelid); - /* ph_needed might or might not become empty */ + /* Reduce ph_needed to contain only "relation 0"; see below */ + if (bms_is_member(0, phinfo->ph_needed)) + phinfo->ph_needed = bms_make_singleton(0); + else + phinfo->ph_needed = NULL; phv->phrels = bms_del_member(phv->phrels, relid); phv->phrels = bms_del_member(phv->phrels, ojrelid); Assert(!bms_is_empty(phv->phrels)); @@ -540,7 +514,7 @@ remove_rel_from_query(PlannerInfo *root, int relid, SpecialJoinInfo *sjinfo) */ /* - * Finally, remove the rel from the baserel array to prevent it from being + * Now remove the rel from the baserel array to prevent it from being * referenced again. (We can't do this earlier because * remove_join_clause_from_rels will touch it.) */ @@ -548,6 +522,51 @@ remove_rel_from_query(PlannerInfo *root, int relid, SpecialJoinInfo *sjinfo) /* And nuke the RelOptInfo, just in case there's another access path */ pfree(rel); + + /* + * Finally, we must recompute per-Var attr_needed and per-PlaceHolderVar + * ph_needed relid sets. These have to be known accurately, else we may + * fail to remove other now-removable outer joins. And our removal of the + * join clause(s) for this outer join may mean that Vars that were + * formerly needed no longer are. So we have to do this honestly by + * repeating the construction of those relid sets. We can cheat to one + * small extent: we can avoid re-examining the targetlist and HAVING qual + * by preserving "relation 0" bits from the existing relid sets. This is + * safe because we'd never remove such references. + * + * So, start by removing all other bits from attr_needed sets. (We + * already did this above for ph_needed.) + */ + for (rti = 1; rti < root->simple_rel_array_size; rti++) + { + RelOptInfo *otherrel = root->simple_rel_array[rti]; + int attroff; + + /* there may be empty slots corresponding to non-baserel RTEs */ + if (otherrel == NULL) + continue; + + Assert(otherrel->relid == rti); /* sanity check on array */ + + for (attroff = otherrel->max_attr - otherrel->min_attr; + attroff >= 0; + attroff--) + { + if (bms_is_member(0, otherrel->attr_needed[attroff])) + otherrel->attr_needed[attroff] = bms_make_singleton(0); + else + otherrel->attr_needed[attroff] = NULL; + } + } + + /* + * Now repeat construction of attr_needed bits coming from all other + * sources. + */ + rebuild_placeholder_attr_needed(root); + rebuild_joinclause_attr_needed(root); + rebuild_eclass_attr_needed(root); + rebuild_lateral_attr_needed(root); } /* diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c index f3b9821498e..c5bc0f51e99 100644 --- a/src/backend/optimizer/plan/initsplan.c +++ b/src/backend/optimizer/plan/initsplan.c @@ -274,6 +274,8 @@ build_base_rel_tlists(PlannerInfo *root, List *final_tlist) * have a single owning relation; we keep their attr_needed info in * root->placeholder_list instead. Find or create the associated * PlaceHolderInfo entry, and update its ph_needed. + * + * See also add_vars_to_attr_needed. */ void add_vars_to_targetlist(PlannerInfo *root, List *vars, @@ -327,6 +329,63 @@ add_vars_to_targetlist(PlannerInfo *root, List *vars, } } +/* + * add_vars_to_attr_needed + * This does a subset of what add_vars_to_targetlist does: it just + * updates attr_needed for Vars and ph_needed for PlaceHolderVars. + * We assume the Vars are already in their relations' targetlists. + * + * This is used to rebuild attr_needed/ph_needed sets after removal + * of a useless outer join. The removed join clause might have been + * the only upper-level use of some other relation's Var, in which + * case we can reduce that Var's attr_needed and thereby possibly + * open the door to further join removals. But we can't tell that + * without tedious reconstruction of the attr_needed data. + * + * Note that if a Var's attr_needed is successfully reduced to empty, + * it will still be in the relation's targetlist even though we do + * not really need the scan plan node to emit it. The extra plan + * inefficiency seems tiny enough to not be worth spending planner + * cycles to get rid of it. + */ +void +add_vars_to_attr_needed(PlannerInfo *root, List *vars, + Relids where_needed) +{ + ListCell *temp; + + Assert(!bms_is_empty(where_needed)); + + foreach(temp, vars) + { + Node *node = (Node *) lfirst(temp); + + if (IsA(node, Var)) + { + Var *var = (Var *) node; + RelOptInfo *rel = find_base_rel(root, var->varno); + int attno = var->varattno; + + if (bms_is_subset(where_needed, rel->relids)) + continue; + Assert(attno >= rel->min_attr && attno <= rel->max_attr); + attno -= rel->min_attr; + rel->attr_needed[attno] = bms_add_members(rel->attr_needed[attno], + where_needed); + } + else if (IsA(node, PlaceHolderVar)) + { + PlaceHolderVar *phv = (PlaceHolderVar *) node; + PlaceHolderInfo *phinfo = find_placeholder_info(root, phv); + + phinfo->ph_needed = bms_add_members(phinfo->ph_needed, + where_needed); + } + else + elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node)); + } +} + /***************************************************************************** * @@ -488,10 +547,54 @@ extract_lateral_references(PlannerInfo *root, RelOptInfo *brel, Index rtindex) */ add_vars_to_targetlist(root, newvars, where_needed); - /* Remember the lateral references for create_lateral_join_info */ + /* + * Remember the lateral references for rebuild_lateral_attr_needed and + * create_lateral_join_info. + */ brel->lateral_vars = newvars; } +/* + * rebuild_lateral_attr_needed + * Put back attr_needed bits for Vars/PHVs needed for lateral references. + * + * This is used to rebuild attr_needed/ph_needed sets after removal of a + * useless outer join. It should match what find_lateral_references did, + * except that we call add_vars_to_attr_needed not add_vars_to_targetlist. + */ +void +rebuild_lateral_attr_needed(PlannerInfo *root) +{ + Index rti; + + /* We need do nothing if the query contains no LATERAL RTEs */ + if (!root->hasLateralRTEs) + return; + + /* Examine the same baserels that find_lateral_references did */ + for (rti = 1; rti < root->simple_rel_array_size; rti++) + { + RelOptInfo *brel = root->simple_rel_array[rti]; + Relids where_needed; + + if (brel == NULL) + continue; + if (brel->reloptkind != RELOPT_BASEREL) + continue; + + /* + * We don't need to repeat all of extract_lateral_references, since it + * kindly saved the extracted Vars/PHVs in lateral_vars. + */ + if (brel->lateral_vars == NIL) + continue; + + where_needed = bms_make_singleton(rti); + + add_vars_to_attr_needed(root, brel->lateral_vars, where_needed); + } +} + /* * create_lateral_join_info * Fill in the per-base-relation direct_lateral_relids, lateral_relids @@ -2445,6 +2548,9 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause, * var propagation is ensured by making ojscope include input rels from * both sides of the join. * + * See also rebuild_joinclause_attr_needed, which has to partially repeat + * this work after removal of an outer join. + * * Note: if the clause gets absorbed into an EquivalenceClass then this * may be unnecessary, but for now we have to do it to cover the case * where the EC becomes ec_broken and we end up reinserting the original @@ -3014,6 +3120,11 @@ process_implied_equality(PlannerInfo *root, * some of the Vars could have missed having that done because they only * appeared in single-relation clauses originally. So do it here for * safety. + * + * See also rebuild_joinclause_attr_needed, which has to partially repeat + * this work after removal of an outer join. (Since we will put this + * clause into the joininfo lists, that function needn't do any extra work + * to find it.) */ if (bms_membership(relids) == BMS_MULTIPLE) { @@ -3155,6 +3266,72 @@ get_join_domain_min_rels(PlannerInfo *root, Relids domain_relids) } +/* + * rebuild_joinclause_attr_needed + * Put back attr_needed bits for Vars/PHVs needed for join clauses. + * + * This is used to rebuild attr_needed/ph_needed sets after removal of a + * useless outer join. It should match what distribute_qual_to_rels did, + * except that we call add_vars_to_attr_needed not add_vars_to_targetlist. + */ +void +rebuild_joinclause_attr_needed(PlannerInfo *root) +{ + /* + * We must examine all join clauses, but there's no value in processing + * any join clause more than once. So it's slightly annoying that we have + * to find them via the per-base-relation joininfo lists. Avoid duplicate + * processing by tracking the rinfo_serial numbers of join clauses we've + * already seen. (This doesn't work for is_clone clauses, so we must + * waste effort on them.) + */ + Bitmapset *seen_serials = NULL; + Index rti; + + /* Scan all baserels for join clauses */ + for (rti = 1; rti < root->simple_rel_array_size; rti++) + { + RelOptInfo *brel = root->simple_rel_array[rti]; + ListCell *lc; + + if (brel == NULL) + continue; + if (brel->reloptkind != RELOPT_BASEREL) + continue; + + foreach(lc, brel->joininfo) + { + RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc); + Relids relids = rinfo->required_relids; + + if (!rinfo->is_clone) /* else serial number is not unique */ + { + if (bms_is_member(rinfo->rinfo_serial, seen_serials)) + continue; /* saw it already */ + seen_serials = bms_add_member(seen_serials, + rinfo->rinfo_serial); + } + + if (bms_membership(relids) == BMS_MULTIPLE) + { + List *vars = pull_var_clause((Node *) rinfo->clause, + PVC_RECURSE_AGGREGATES | + PVC_RECURSE_WINDOWFUNCS | + PVC_INCLUDE_PLACEHOLDERS); + Relids where_needed; + + if (rinfo->is_clone) + where_needed = bms_intersect(relids, root->all_baserels); + else + where_needed = relids; + add_vars_to_attr_needed(root, vars, where_needed); + list_free(vars); + } + } + } +} + + /* * match_foreign_keys_to_quals * Match foreign-key constraints to equivalence classes and join quals diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c index 81abadd6db3..cce90865315 100644 --- a/src/backend/optimizer/util/placeholder.c +++ b/src/backend/optimizer/util/placeholder.c @@ -314,6 +314,33 @@ fix_placeholder_input_needed_levels(PlannerInfo *root) } } +/* + * rebuild_placeholder_attr_needed + * Put back attr_needed bits for Vars/PHVs needed in PlaceHolderVars. + * + * This is used to rebuild attr_needed/ph_needed sets after removal of a + * useless outer join. It should match what + * fix_placeholder_input_needed_levels did, except that we call + * add_vars_to_attr_needed not add_vars_to_targetlist. + */ +void +rebuild_placeholder_attr_needed(PlannerInfo *root) +{ + ListCell *lc; + + foreach(lc, root->placeholder_list) + { + PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc); + List *vars = pull_var_clause((Node *) phinfo->ph_var->phexpr, + PVC_RECURSE_AGGREGATES | + PVC_RECURSE_WINDOWFUNCS | + PVC_INCLUDE_PLACEHOLDERS); + + add_vars_to_attr_needed(root, vars, phinfo->ph_eval_at); + list_free(vars); + } +} + /* * add_placeholders_to_base_rels * Add any required PlaceHolderVars to base rels' targetlists. diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h index a78e90610fc..54869d44013 100644 --- a/src/include/optimizer/paths.h +++ b/src/include/optimizer/paths.h @@ -128,6 +128,7 @@ extern bool process_equivalence(PlannerInfo *root, extern Expr *canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation); extern void reconsider_outer_join_clauses(PlannerInfo *root); +extern void rebuild_eclass_attr_needed(PlannerInfo *root); extern EquivalenceClass *get_eclass_for_sort_expr(PlannerInfo *root, Expr *expr, List *opfamilies, diff --git a/src/include/optimizer/placeholder.h b/src/include/optimizer/placeholder.h index d8610863fc5..97c12eae03e 100644 --- a/src/include/optimizer/placeholder.h +++ b/src/include/optimizer/placeholder.h @@ -23,6 +23,7 @@ extern PlaceHolderInfo *find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv); extern void find_placeholders_in_jointree(PlannerInfo *root); extern void fix_placeholder_input_needed_levels(PlannerInfo *root); +extern void rebuild_placeholder_attr_needed(PlannerInfo *root); extern void add_placeholders_to_base_rels(PlannerInfo *root); extern void add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outer_rel, RelOptInfo *inner_rel, diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h index aafc1737921..93137261e48 100644 --- a/src/include/optimizer/planmain.h +++ b/src/include/optimizer/planmain.h @@ -72,7 +72,10 @@ extern void add_other_rels_to_query(PlannerInfo *root); extern void build_base_rel_tlists(PlannerInfo *root, List *final_tlist); extern void add_vars_to_targetlist(PlannerInfo *root, List *vars, Relids where_needed); +extern void add_vars_to_attr_needed(PlannerInfo *root, List *vars, + Relids where_needed); extern void find_lateral_references(PlannerInfo *root); +extern void rebuild_lateral_attr_needed(PlannerInfo *root); extern void create_lateral_join_info(PlannerInfo *root); extern List *deconstruct_jointree(PlannerInfo *root); extern bool restriction_is_always_true(PlannerInfo *root, @@ -96,6 +99,7 @@ extern RestrictInfo *build_implied_join_equality(PlannerInfo *root, Expr *item2, Relids qualscope, Index security_level); +extern void rebuild_joinclause_attr_needed(PlannerInfo *root); extern void match_foreign_keys_to_quals(PlannerInfo *root); /* diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out index 31fb7d142eb..12abd3a0e7a 100644 --- a/src/test/regress/expected/join.out +++ b/src/test/regress/expected/join.out @@ -5457,11 +5457,13 @@ CREATE TEMP TABLE a (id int PRIMARY KEY, b_id int); CREATE TEMP TABLE b (id int PRIMARY KEY, c_id int); CREATE TEMP TABLE c (id int PRIMARY KEY); CREATE TEMP TABLE d (a int, b int); +CREATE TEMP TABLE e (id1 int, id2 int, PRIMARY KEY(id1, id2)); INSERT INTO a VALUES (0, 0), (1, NULL); INSERT INTO b VALUES (0, 0), (1, NULL); INSERT INTO c VALUES (0), (1); INSERT INTO d VALUES (1,3), (2,2), (3,1); --- all three cases should be optimizable into a simple seqscan +INSERT INTO e VALUES (0,0), (2,2), (3,1); +-- all these cases should be optimizable into a simple seqscan explain (costs off) SELECT a.* FROM a LEFT JOIN b ON a.b_id = b.id; QUERY PLAN --------------- @@ -5482,6 +5484,14 @@ explain (costs off) Seq Scan on a (1 row) +explain (costs off) + SELECT a.* FROM a LEFT JOIN b ON a.id = b.id + LEFT JOIN e ON e.id1 = a.b_id AND b.c_id = e.id2; + QUERY PLAN +--------------- + Seq Scan on a +(1 row) + -- check optimization of outer join within another special join explain (costs off) select id from a where id in ( diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql index d81ff63be53..0c65e5af4be 100644 --- a/src/test/regress/sql/join.sql +++ b/src/test/regress/sql/join.sql @@ -1952,17 +1952,22 @@ CREATE TEMP TABLE a (id int PRIMARY KEY, b_id int); CREATE TEMP TABLE b (id int PRIMARY KEY, c_id int); CREATE TEMP TABLE c (id int PRIMARY KEY); CREATE TEMP TABLE d (a int, b int); +CREATE TEMP TABLE e (id1 int, id2 int, PRIMARY KEY(id1, id2)); INSERT INTO a VALUES (0, 0), (1, NULL); INSERT INTO b VALUES (0, 0), (1, NULL); INSERT INTO c VALUES (0), (1); INSERT INTO d VALUES (1,3), (2,2), (3,1); +INSERT INTO e VALUES (0,0), (2,2), (3,1); --- all three cases should be optimizable into a simple seqscan +-- all these cases should be optimizable into a simple seqscan explain (costs off) SELECT a.* FROM a LEFT JOIN b ON a.b_id = b.id; explain (costs off) SELECT b.* FROM b LEFT JOIN c ON b.c_id = c.id; explain (costs off) SELECT a.* FROM a LEFT JOIN (b left join c on b.c_id = c.id) ON (a.b_id = b.id); +explain (costs off) + SELECT a.* FROM a LEFT JOIN b ON a.id = b.id + LEFT JOIN e ON e.id1 = a.b_id AND b.c_id = e.id2; -- check optimization of outer join within another special join explain (costs off)