1 /*-------------------------------------------------------------------------
4 * Routines copied from PostgreSQL core distribution.
7 * The main purpose of this files is having access to static functions in core.
8 * Another purpose is tweaking functions behavior by replacing part of them by
9 * macro definitions. See at the end of pg_hint_plan.c for details. Anyway,
10 * this file *must* contain required functions without making any change.
12 * This file contains the following functions from corresponding files.
14 * src/backend/optimizer/path/allpaths.c
17 * set_plain_rel_pathlist()
18 * create_plain_partial_paths()
19 * set_append_rel_pathlist()
20 * add_paths_to_append_rel()
21 * generate_mergeappend_paths()
22 * get_cheapest_parameterized_child_path()
23 * accumulate_append_subpath()
26 * standard_join_search(): This funcion is not static. The reason for
27 * including this function is make_rels_by_clause_joins. In order to
28 * avoid generating apparently unwanted join combination, we decided to
29 * change the behavior of make_join_rel, which is called under this
32 * src/backend/optimizer/path/joinrels.c
35 * join_search_one_level(): We have to modify this to call my definition of
36 * make_rels_by_clause_joins.
39 * make_rels_by_clause_joins()
40 * make_rels_by_clauseless_joins()
42 * has_join_restriction()
44 * restriction_is_constant_false()
47 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
48 * Portions Copyright (c) 1994, Regents of the University of California
50 *-------------------------------------------------------------------------
55 * set_plain_rel_pathlist
56 * Build access paths for a plain relation (no subquery, no inheritance)
59 set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
61 Relids required_outer;
64 * We don't support pushing join clauses into the quals of a seqscan, but
65 * it could still have required parameterization due to LATERAL refs in
68 required_outer = rel->lateral_relids;
70 /* Consider sequential scan */
71 add_path(rel, create_seqscan_path(root, rel, required_outer, 0));
73 /* If appropriate, consider parallel sequential scan */
74 if (rel->consider_parallel && required_outer == NULL)
75 create_plain_partial_paths(root, rel);
77 /* Consider index scans */
78 create_index_paths(root, rel);
80 /* Consider TID scans */
81 create_tidscan_paths(root, rel);
86 * create_plain_partial_paths
87 * Build partial access paths for parallel scan of a plain relation
90 create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
94 parallel_workers = compute_parallel_worker(rel, rel->pages, -1);
96 /* If any limit was set to zero, the user doesn't want a parallel scan. */
97 if (parallel_workers <= 0)
100 /* Add an unordered partial path based on a parallel sequential scan. */
101 add_partial_path(rel, create_seqscan_path(root, rel, NULL, parallel_workers));
106 * set_append_rel_pathlist
107 * Build access paths for an "append relation"
110 set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
111 Index rti, RangeTblEntry *rte)
113 int parentRTindex = rti;
114 List *live_childrels = NIL;
118 * Generate access paths for each member relation, and remember the
119 * non-dummy children.
121 foreach(l, root->append_rel_list)
123 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
125 RangeTblEntry *childRTE;
126 RelOptInfo *childrel;
128 /* append_rel_list contains all append rels; ignore others */
129 if (appinfo->parent_relid != parentRTindex)
132 /* Re-locate the child RTE and RelOptInfo */
133 childRTindex = appinfo->child_relid;
134 childRTE = root->simple_rte_array[childRTindex];
135 childrel = root->simple_rel_array[childRTindex];
138 * If set_append_rel_size() decided the parent appendrel was
139 * parallel-unsafe at some point after visiting this child rel, we
140 * need to propagate the unsafety marking down to the child, so that
141 * we don't generate useless partial paths for it.
143 if (!rel->consider_parallel)
144 childrel->consider_parallel = false;
147 * Compute the child's access paths.
149 set_rel_pathlist(root, childrel, childRTindex, childRTE);
152 * If child is dummy, ignore it.
154 if (IS_DUMMY_REL(childrel))
158 * Child is live, so add it to the live_childrels list for use below.
160 live_childrels = lappend(live_childrels, childrel);
163 /* Add paths to the "append" relation. */
164 add_paths_to_append_rel(root, rel, live_childrels);
168 * add_paths_to_append_rel
169 * Generate paths for given "append" relation given the set of non-dummy
172 * The function collects all parameterizations and orderings supported by the
173 * non-dummy children. For every such parameterization or ordering, it creates
174 * an append path collecting one path from each non-dummy child with given
175 * parameterization or ordering. Similarly it collects partial paths from
176 * non-dummy children to create partial append paths.
179 add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
180 List *live_childrels)
182 List *subpaths = NIL;
183 bool subpaths_valid = true;
184 List *partial_subpaths = NIL;
185 bool partial_subpaths_valid = true;
186 List *all_child_pathkeys = NIL;
187 List *all_child_outers = NIL;
189 List *partitioned_rels = NIL;
191 bool build_partitioned_rels = false;
194 * A plain relation will already have a PartitionedChildRelInfo if it is
195 * partitioned. For a subquery RTE, no PartitionedChildRelInfo exists; we
196 * collect all partitioned_rels associated with any child. (This assumes
197 * that we don't need to look through multiple levels of subquery RTEs; if
198 * we ever do, we could create a PartitionedChildRelInfo with the
199 * accumulated list of partitioned_rels which would then be found when
200 * populated our parent rel with paths. For the present, that appears to
203 rte = planner_rt_fetch(rel->relid, root);
204 switch (rte->rtekind)
207 if (rte->relkind == RELKIND_PARTITIONED_TABLE)
210 get_partitioned_child_rels(root, rel->relid);
211 Assert(list_length(partitioned_rels) >= 1);
215 build_partitioned_rels = true;
218 elog(ERROR, "unexpected rtekind: %d", (int) rte->rtekind);
222 * For every non-dummy child, remember the cheapest path. Also, identify
223 * all pathkeys (orderings) and parameterizations (required_outer sets)
224 * available for the non-dummy member relations.
226 foreach(l, live_childrels)
228 RelOptInfo *childrel = lfirst(l);
232 * If we need to build partitioned_rels, accumulate the partitioned
233 * rels for this child.
235 if (build_partitioned_rels)
239 cprels = get_partitioned_child_rels(root, childrel->relid);
240 partitioned_rels = list_concat(partitioned_rels,
245 * If child has an unparameterized cheapest-total path, add that to
246 * the unparameterized Append path we are constructing for the parent.
247 * If not, there's no workable unparameterized path.
249 if (childrel->cheapest_total_path->param_info == NULL)
250 subpaths = accumulate_append_subpath(subpaths,
251 childrel->cheapest_total_path);
253 subpaths_valid = false;
255 /* Same idea, but for a partial plan. */
256 if (childrel->partial_pathlist != NIL)
257 partial_subpaths = accumulate_append_subpath(partial_subpaths,
258 linitial(childrel->partial_pathlist));
260 partial_subpaths_valid = false;
263 * Collect lists of all the available path orderings and
264 * parameterizations for all the children. We use these as a
265 * heuristic to indicate which sort orderings and parameterizations we
266 * should build Append and MergeAppend paths for.
268 foreach(lcp, childrel->pathlist)
270 Path *childpath = (Path *) lfirst(lcp);
271 List *childkeys = childpath->pathkeys;
272 Relids childouter = PATH_REQ_OUTER(childpath);
274 /* Unsorted paths don't contribute to pathkey list */
275 if (childkeys != NIL)
280 /* Have we already seen this ordering? */
281 foreach(lpk, all_child_pathkeys)
283 List *existing_pathkeys = (List *) lfirst(lpk);
285 if (compare_pathkeys(existing_pathkeys,
286 childkeys) == PATHKEYS_EQUAL)
294 /* No, so add it to all_child_pathkeys */
295 all_child_pathkeys = lappend(all_child_pathkeys,
300 /* Unparameterized paths don't contribute to param-set list */
306 /* Have we already seen this param set? */
307 foreach(lco, all_child_outers)
309 Relids existing_outers = (Relids) lfirst(lco);
311 if (bms_equal(existing_outers, childouter))
319 /* No, so add it to all_child_outers */
320 all_child_outers = lappend(all_child_outers,
328 * If we found unparameterized paths for all children, build an unordered,
329 * unparameterized Append path for the rel. (Note: this is correct even
330 * if we have zero or one live subpath due to constraint exclusion.)
333 add_path(rel, (Path *) create_append_path(rel, subpaths, NULL, 0,
337 * Consider an append of partial unordered, unparameterized partial paths.
339 if (partial_subpaths_valid && partial_subpaths != NIL)
341 AppendPath *appendpath;
343 int parallel_workers = 0;
346 * Decide on the number of workers to request for this append path.
347 * For now, we just use the maximum value from among the members. It
348 * might be useful to use a higher number if the Append node were
349 * smart enough to spread out the workers, but it currently isn't.
351 foreach(lc, partial_subpaths)
353 Path *path = lfirst(lc);
355 parallel_workers = Max(parallel_workers, path->parallel_workers);
357 Assert(parallel_workers > 0);
359 /* Generate a partial append path. */
360 appendpath = create_append_path(rel, partial_subpaths, NULL,
361 parallel_workers, partitioned_rels);
362 add_partial_path(rel, (Path *) appendpath);
366 * Also build unparameterized MergeAppend paths based on the collected
367 * list of child pathkeys.
370 generate_mergeappend_paths(root, rel, live_childrels,
375 * Build Append paths for each parameterization seen among the child rels.
376 * (This may look pretty expensive, but in most cases of practical
377 * interest, the child rels will expose mostly the same parameterizations,
378 * so that not that many cases actually get considered here.)
380 * The Append node itself cannot enforce quals, so all qual checking must
381 * be done in the child paths. This means that to have a parameterized
382 * Append path, we must have the exact same parameterization for each
383 * child path; otherwise some children might be failing to check the
384 * moved-down quals. To make them match up, we can try to increase the
385 * parameterization of lesser-parameterized paths.
387 foreach(l, all_child_outers)
389 Relids required_outer = (Relids) lfirst(l);
392 /* Select the child paths for an Append with this parameterization */
394 subpaths_valid = true;
395 foreach(lcr, live_childrels)
397 RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
400 subpath = get_cheapest_parameterized_child_path(root,
405 /* failed to make a suitable path for this child */
406 subpaths_valid = false;
409 subpaths = accumulate_append_subpath(subpaths, subpath);
413 add_path(rel, (Path *)
414 create_append_path(rel, subpaths, required_outer, 0,
421 * generate_mergeappend_paths
422 * Generate MergeAppend paths for an append relation
424 * Generate a path for each ordering (pathkey list) appearing in
425 * all_child_pathkeys.
427 * We consider both cheapest-startup and cheapest-total cases, ie, for each
428 * interesting ordering, collect all the cheapest startup subpaths and all the
429 * cheapest total paths, and build a MergeAppend path for each case.
431 * We don't currently generate any parameterized MergeAppend paths. While
432 * it would not take much more code here to do so, it's very unclear that it
433 * is worth the planning cycles to investigate such paths: there's little
434 * use for an ordered path on the inside of a nestloop. In fact, it's likely
435 * that the current coding of add_path would reject such paths out of hand,
436 * because add_path gives no credit for sort ordering of parameterized paths,
437 * and a parameterized MergeAppend is going to be more expensive than the
438 * corresponding parameterized Append path. If we ever try harder to support
439 * parameterized mergejoin plans, it might be worth adding support for
440 * parameterized MergeAppends to feed such joins. (See notes in
441 * optimizer/README for why that might not ever happen, though.)
444 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
445 List *live_childrels,
446 List *all_child_pathkeys,
447 List *partitioned_rels)
451 foreach(lcp, all_child_pathkeys)
453 List *pathkeys = (List *) lfirst(lcp);
454 List *startup_subpaths = NIL;
455 List *total_subpaths = NIL;
456 bool startup_neq_total = false;
459 /* Select the child paths for this ordering... */
460 foreach(lcr, live_childrels)
462 RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
463 Path *cheapest_startup,
466 /* Locate the right paths, if they are available. */
468 get_cheapest_path_for_pathkeys(childrel->pathlist,
474 get_cheapest_path_for_pathkeys(childrel->pathlist,
481 * If we can't find any paths with the right order just use the
482 * cheapest-total path; we'll have to sort it later.
484 if (cheapest_startup == NULL || cheapest_total == NULL)
486 cheapest_startup = cheapest_total =
487 childrel->cheapest_total_path;
488 /* Assert we do have an unparameterized path for this child */
489 Assert(cheapest_total->param_info == NULL);
493 * Notice whether we actually have different paths for the
494 * "cheapest" and "total" cases; frequently there will be no point
495 * in two create_merge_append_path() calls.
497 if (cheapest_startup != cheapest_total)
498 startup_neq_total = true;
501 accumulate_append_subpath(startup_subpaths, cheapest_startup);
503 accumulate_append_subpath(total_subpaths, cheapest_total);
506 /* ... and build the MergeAppend paths */
507 add_path(rel, (Path *) create_merge_append_path(root,
513 if (startup_neq_total)
514 add_path(rel, (Path *) create_merge_append_path(root,
525 * get_cheapest_parameterized_child_path
526 * Get cheapest path for this relation that has exactly the requested
529 * Returns NULL if unable to create such a path.
532 get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
533 Relids required_outer)
539 * Look up the cheapest existing path with no more than the needed
540 * parameterization. If it has exactly the needed parameterization, we're
543 cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
548 Assert(cheapest != NULL);
549 if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
553 * Otherwise, we can "reparameterize" an existing path to match the given
554 * parameterization, which effectively means pushing down additional
555 * joinquals to be checked within the path's scan. However, some existing
556 * paths might check the available joinquals already while others don't;
557 * therefore, it's not clear which existing path will be cheapest after
558 * reparameterization. We have to go through them all and find out.
561 foreach(lc, rel->pathlist)
563 Path *path = (Path *) lfirst(lc);
565 /* Can't use it if it needs more than requested parameterization */
566 if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
570 * Reparameterization can only increase the path's cost, so if it's
571 * already more expensive than the current cheapest, forget it.
573 if (cheapest != NULL &&
574 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
577 /* Reparameterize if needed, then recheck cost */
578 if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
580 path = reparameterize_path(root, path, required_outer, 1.0);
582 continue; /* failed to reparameterize this one */
583 Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));
585 if (cheapest != NULL &&
586 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
590 /* We have a new best path */
594 /* Return the best path, or NULL if we found no suitable candidate */
600 * accumulate_append_subpath
601 * Add a subpath to the list being built for an Append or MergeAppend
603 * It's possible that the child is itself an Append or MergeAppend path, in
604 * which case we can "cut out the middleman" and just add its child paths to
605 * our own list. (We don't try to do this earlier because we need to apply
606 * both levels of transformation to the quals.)
608 * Note that if we omit a child MergeAppend in this way, we are effectively
609 * omitting a sort step, which seems fine: if the parent is to be an Append,
610 * its result would be unsorted anyway, while if the parent is to be a
611 * MergeAppend, there's no point in a separate sort on a child.
614 accumulate_append_subpath(List *subpaths, Path *path)
616 if (IsA(path, AppendPath))
618 AppendPath *apath = (AppendPath *) path;
620 /* list_copy is important here to avoid sharing list substructure */
621 return list_concat(subpaths, list_copy(apath->subpaths));
623 else if (IsA(path, MergeAppendPath))
625 MergeAppendPath *mpath = (MergeAppendPath *) path;
627 /* list_copy is important here to avoid sharing list substructure */
628 return list_concat(subpaths, list_copy(mpath->subpaths));
631 return lappend(subpaths, path);
636 * standard_join_search
637 * Find possible joinpaths for a query by successively finding ways
638 * to join component relations into join relations.
640 * 'levels_needed' is the number of iterations needed, ie, the number of
641 * independent jointree items in the query. This is > 1.
643 * 'initial_rels' is a list of RelOptInfo nodes for each independent
644 * jointree item. These are the components to be joined together.
645 * Note that levels_needed == list_length(initial_rels).
647 * Returns the final level of join relations, i.e., the relation that is
648 * the result of joining all the original relations together.
649 * At least one implementation path must be provided for this relation and
650 * all required sub-relations.
652 * To support loadable plugins that modify planner behavior by changing the
653 * join searching algorithm, we provide a hook variable that lets a plugin
654 * replace or supplement this function. Any such hook must return the same
655 * final join relation as the standard code would, but it might have a
656 * different set of implementation paths attached, and only the sub-joinrels
657 * needed for these paths need have been instantiated.
659 * Note to plugin authors: the functions invoked during standard_join_search()
660 * modify root->join_rel_list and root->join_rel_hash. If you want to do more
661 * than one join-order search, you'll probably need to save and restore the
662 * original states of those data structures. See geqo_eval() for an example.
665 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
671 * This function cannot be invoked recursively within any one planning
672 * problem, so join_rel_level[] can't be in use already.
674 Assert(root->join_rel_level == NULL);
677 * We employ a simple "dynamic programming" algorithm: we first find all
678 * ways to build joins of two jointree items, then all ways to build joins
679 * of three items (from two-item joins and single items), then four-item
680 * joins, and so on until we have considered all ways to join all the
681 * items into one rel.
683 * root->join_rel_level[j] is a list of all the j-item rels. Initially we
684 * set root->join_rel_level[1] to represent all the single-jointree-item
687 root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
689 root->join_rel_level[1] = initial_rels;
691 for (lev = 2; lev <= levels_needed; lev++)
696 * Determine all possible pairs of relations to be joined at this
697 * level, and build paths for making each one from every available
698 * pair of lower-level relations.
700 join_search_one_level(root, lev);
703 * Run generate_gather_paths() for each just-processed joinrel. We
704 * could not do this earlier because both regular and partial paths
705 * can get added to a particular joinrel at multiple times within
706 * join_search_one_level. After that, we're done creating paths for
707 * the joinrel, so run set_cheapest().
709 foreach(lc, root->join_rel_level[lev])
711 rel = (RelOptInfo *) lfirst(lc);
713 /* Create GatherPaths for any useful partial paths for rel */
714 generate_gather_paths(root, rel);
716 /* Find and save the cheapest paths for this rel */
719 #ifdef OPTIMIZER_DEBUG
720 debug_print_rel(root, rel);
726 * We should have a single rel at the final level.
728 if (root->join_rel_level[levels_needed] == NIL)
729 elog(ERROR, "failed to build any %d-way joins", levels_needed);
730 Assert(list_length(root->join_rel_level[levels_needed]) == 1);
732 rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
734 root->join_rel_level = NULL;
741 * join_search_one_level
742 * Consider ways to produce join relations containing exactly 'level'
743 * jointree items. (This is one step of the dynamic-programming method
744 * embodied in standard_join_search.) Join rel nodes for each feasible
745 * combination of lower-level rels are created and returned in a list.
746 * Implementation paths are created for each such joinrel, too.
748 * level: level of rels we want to make this time
749 * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
751 * The result is returned in root->join_rel_level[level].
754 join_search_one_level(PlannerInfo *root, int level)
756 List **joinrels = root->join_rel_level;
760 Assert(joinrels[level] == NIL);
762 /* Set join_cur_level so that new joinrels are added to proper list */
763 root->join_cur_level = level;
766 * First, consider left-sided and right-sided plans, in which rels of
767 * exactly level-1 member relations are joined against initial relations.
768 * We prefer to join using join clauses, but if we find a rel of level-1
769 * members that has no join clauses, we will generate Cartesian-product
770 * joins against all initial rels not already contained in it.
772 foreach(r, joinrels[level - 1])
774 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
776 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
777 has_join_restriction(root, old_rel))
780 * There are join clauses or join order restrictions relevant to
781 * this rel, so consider joins between this rel and (only) those
782 * initial rels it is linked to by a clause or restriction.
784 * At level 2 this condition is symmetric, so there is no need to
785 * look at initial rels before this one in the list; we already
786 * considered such joins when we were at the earlier rel. (The
787 * mirror-image joins are handled automatically by make_join_rel.)
788 * In later passes (level > 2), we join rels of the previous level
789 * to each initial rel they don't already include but have a join
790 * clause or restriction with.
792 ListCell *other_rels;
794 if (level == 2) /* consider remaining initial rels */
795 other_rels = lnext(r);
796 else /* consider all initial rels */
797 other_rels = list_head(joinrels[1]);
799 make_rels_by_clause_joins(root,
806 * Oops, we have a relation that is not joined to any other
807 * relation, either directly or by join-order restrictions.
808 * Cartesian product time.
810 * We consider a cartesian product with each not-already-included
811 * initial rel, whether it has other join clauses or not. At
812 * level 2, if there are two or more clauseless initial rels, we
813 * will redundantly consider joining them in both directions; but
814 * such cases aren't common enough to justify adding complexity to
815 * avoid the duplicated effort.
817 make_rels_by_clauseless_joins(root,
819 list_head(joinrels[1]));
824 * Now, consider "bushy plans" in which relations of k initial rels are
825 * joined to relations of level-k initial rels, for 2 <= k <= level-2.
827 * We only consider bushy-plan joins for pairs of rels where there is a
828 * suitable join clause (or join order restriction), in order to avoid
829 * unreasonable growth of planning time.
833 int other_level = level - k;
836 * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
837 * need to go as far as the halfway point.
842 foreach(r, joinrels[k])
844 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
845 ListCell *other_rels;
849 * We can ignore relations without join clauses here, unless they
850 * participate in join-order restrictions --- then we might have
851 * to force a bushy join plan.
853 if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
854 !has_join_restriction(root, old_rel))
857 if (k == other_level)
858 other_rels = lnext(r); /* only consider remaining rels */
860 other_rels = list_head(joinrels[other_level]);
862 for_each_cell(r2, other_rels)
864 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
866 if (!bms_overlap(old_rel->relids, new_rel->relids))
869 * OK, we can build a rel of the right level from this
870 * pair of rels. Do so if there is at least one relevant
871 * join clause or join order restriction.
873 if (have_relevant_joinclause(root, old_rel, new_rel) ||
874 have_join_order_restriction(root, old_rel, new_rel))
876 (void) make_join_rel(root, old_rel, new_rel);
884 * Last-ditch effort: if we failed to find any usable joins so far, force
885 * a set of cartesian-product joins to be generated. This handles the
886 * special case where all the available rels have join clauses but we
887 * cannot use any of those clauses yet. This can only happen when we are
888 * considering a join sub-problem (a sub-joinlist) and all the rels in the
889 * sub-problem have only join clauses with rels outside the sub-problem.
892 * SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
893 * WHERE a.w = c.x and b.y = d.z;
895 * If the "a INNER JOIN b" sub-problem does not get flattened into the
896 * upper level, we must be willing to make a cartesian join of a and b;
897 * but the code above will not have done so, because it thought that both
898 * a and b have joinclauses. We consider only left-sided and right-sided
899 * cartesian joins in this case (no bushy).
902 if (joinrels[level] == NIL)
905 * This loop is just like the first one, except we always call
906 * make_rels_by_clauseless_joins().
908 foreach(r, joinrels[level - 1])
910 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
912 make_rels_by_clauseless_joins(root,
914 list_head(joinrels[1]));
918 * When special joins are involved, there may be no legal way
919 * to make an N-way join for some values of N. For example consider
921 * SELECT ... FROM t1 WHERE
922 * x IN (SELECT ... FROM t2,t3 WHERE ...) AND
923 * y IN (SELECT ... FROM t4,t5 WHERE ...)
925 * We will flatten this query to a 5-way join problem, but there are
926 * no 4-way joins that join_is_legal() will consider legal. We have
927 * to accept failure at level 4 and go on to discover a workable
928 * bushy plan at level 5.
930 * However, if there are no special joins and no lateral references
931 * then join_is_legal() should never fail, and so the following sanity
935 if (joinrels[level] == NIL &&
936 root->join_info_list == NIL &&
937 !root->hasLateralRTEs)
938 elog(ERROR, "failed to build any %d-way joins", level);
944 * make_rels_by_clause_joins
945 * Build joins between the given relation 'old_rel' and other relations
946 * that participate in join clauses that 'old_rel' also participates in
947 * (or participate in join-order restrictions with it).
948 * The join rels are returned in root->join_rel_level[join_cur_level].
950 * Note: at levels above 2 we will generate the same joined relation in
951 * multiple ways --- for example (a join b) join c is the same RelOptInfo as
952 * (b join c) join a, though the second case will add a different set of Paths
953 * to it. This is the reason for using the join_rel_level mechanism, which
954 * automatically ensures that each new joinrel is only added to the list once.
956 * 'old_rel' is the relation entry for the relation to be joined
957 * 'other_rels': the first cell in a linked list containing the other
958 * rels to be considered for joining
960 * Currently, this is only used with initial rels in other_rels, but it
961 * will work for joining to joinrels too.
964 make_rels_by_clause_joins(PlannerInfo *root,
966 ListCell *other_rels)
970 for_each_cell(l, other_rels)
972 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
974 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
975 (have_relevant_joinclause(root, old_rel, other_rel) ||
976 have_join_order_restriction(root, old_rel, other_rel)))
978 (void) make_join_rel(root, old_rel, other_rel);
985 * make_rels_by_clauseless_joins
986 * Given a relation 'old_rel' and a list of other relations
987 * 'other_rels', create a join relation between 'old_rel' and each
988 * member of 'other_rels' that isn't already included in 'old_rel'.
989 * The join rels are returned in root->join_rel_level[join_cur_level].
991 * 'old_rel' is the relation entry for the relation to be joined
992 * 'other_rels': the first cell of a linked list containing the
993 * other rels to be considered for joining
995 * Currently, this is only used with initial rels in other_rels, but it would
996 * work for joining to joinrels too.
999 make_rels_by_clauseless_joins(PlannerInfo *root,
1000 RelOptInfo *old_rel,
1001 ListCell *other_rels)
1005 for_each_cell(l, other_rels)
1007 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
1009 if (!bms_overlap(other_rel->relids, old_rel->relids))
1011 (void) make_join_rel(root, old_rel, other_rel);
1019 * Determine whether a proposed join is legal given the query's
1020 * join order constraints; and if it is, determine the join type.
1022 * Caller must supply not only the two rels, but the union of their relids.
1023 * (We could simplify the API by computing joinrelids locally, but this
1024 * would be redundant work in the normal path through make_join_rel.)
1026 * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
1027 * else it's set to point to the associated SpecialJoinInfo node. Also,
1028 * *reversed_p is set TRUE if the given relations need to be swapped to
1029 * match the SpecialJoinInfo node.
1032 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
1034 SpecialJoinInfo **sjinfo_p, bool *reversed_p)
1036 SpecialJoinInfo *match_sjinfo;
1039 bool must_be_leftjoin;
1043 * Ensure output params are set on failure return. This is just to
1044 * suppress uninitialized-variable warnings from overly anal compilers.
1047 *reversed_p = false;
1050 * If we have any special joins, the proposed join might be illegal; and
1051 * in any case we have to determine its join type. Scan the join info
1052 * list for matches and conflicts.
1054 match_sjinfo = NULL;
1056 unique_ified = false;
1057 must_be_leftjoin = false;
1059 foreach(l, root->join_info_list)
1061 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1064 * This special join is not relevant unless its RHS overlaps the
1065 * proposed join. (Check this first as a fast path for dismissing
1066 * most irrelevant SJs quickly.)
1068 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
1072 * Also, not relevant if proposed join is fully contained within RHS
1073 * (ie, we're still building up the RHS).
1075 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
1079 * Also, not relevant if SJ is already done within either input.
1081 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
1082 bms_is_subset(sjinfo->min_righthand, rel1->relids))
1084 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
1085 bms_is_subset(sjinfo->min_righthand, rel2->relids))
1089 * If it's a semijoin and we already joined the RHS to any other rels
1090 * within either input, then we must have unique-ified the RHS at that
1091 * point (see below). Therefore the semijoin is no longer relevant in
1094 if (sjinfo->jointype == JOIN_SEMI)
1096 if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
1097 !bms_equal(sjinfo->syn_righthand, rel1->relids))
1099 if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
1100 !bms_equal(sjinfo->syn_righthand, rel2->relids))
1105 * If one input contains min_lefthand and the other contains
1106 * min_righthand, then we can perform the SJ at this join.
1108 * Reject if we get matches to more than one SJ; that implies we're
1109 * considering something that's not really valid.
1111 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
1112 bms_is_subset(sjinfo->min_righthand, rel2->relids))
1115 return false; /* invalid join path */
1116 match_sjinfo = sjinfo;
1119 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
1120 bms_is_subset(sjinfo->min_righthand, rel1->relids))
1123 return false; /* invalid join path */
1124 match_sjinfo = sjinfo;
1127 else if (sjinfo->jointype == JOIN_SEMI &&
1128 bms_equal(sjinfo->syn_righthand, rel2->relids) &&
1129 create_unique_path(root, rel2, rel2->cheapest_total_path,
1133 * For a semijoin, we can join the RHS to anything else by
1134 * unique-ifying the RHS (if the RHS can be unique-ified).
1135 * We will only get here if we have the full RHS but less
1136 * than min_lefthand on the LHS.
1138 * The reason to consider such a join path is exemplified by
1139 * SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
1140 * If we insist on doing this as a semijoin we will first have
1141 * to form the cartesian product of A*B. But if we unique-ify
1142 * C then the semijoin becomes a plain innerjoin and we can join
1143 * in any order, eg C to A and then to B. When C is much smaller
1144 * than A and B this can be a huge win. So we allow C to be
1145 * joined to just A or just B here, and then make_join_rel has
1146 * to handle the case properly.
1148 * Note that actually we'll allow unique-ified C to be joined to
1149 * some other relation D here, too. That is legal, if usually not
1150 * very sane, and this routine is only concerned with legality not
1151 * with whether the join is good strategy.
1155 return false; /* invalid join path */
1156 match_sjinfo = sjinfo;
1158 unique_ified = true;
1160 else if (sjinfo->jointype == JOIN_SEMI &&
1161 bms_equal(sjinfo->syn_righthand, rel1->relids) &&
1162 create_unique_path(root, rel1, rel1->cheapest_total_path,
1165 /* Reversed semijoin case */
1167 return false; /* invalid join path */
1168 match_sjinfo = sjinfo;
1170 unique_ified = true;
1175 * Otherwise, the proposed join overlaps the RHS but isn't a valid
1176 * implementation of this SJ. But don't panic quite yet: the RHS
1177 * violation might have occurred previously, in one or both input
1178 * relations, in which case we must have previously decided that
1179 * it was OK to commute some other SJ with this one. If we need
1180 * to perform this join to finish building up the RHS, rejecting
1181 * it could lead to not finding any plan at all. (This can occur
1182 * because of the heuristics elsewhere in this file that postpone
1183 * clauseless joins: we might not consider doing a clauseless join
1184 * within the RHS until after we've performed other, validly
1185 * commutable SJs with one or both sides of the clauseless join.)
1186 * This consideration boils down to the rule that if both inputs
1187 * overlap the RHS, we can allow the join --- they are either
1188 * fully within the RHS, or represent previously-allowed joins to
1191 if (bms_overlap(rel1->relids, sjinfo->min_righthand) &&
1192 bms_overlap(rel2->relids, sjinfo->min_righthand))
1193 continue; /* assume valid previous violation of RHS */
1196 * The proposed join could still be legal, but only if we're
1197 * allowed to associate it into the RHS of this SJ. That means
1198 * this SJ must be a LEFT join (not SEMI or ANTI, and certainly
1199 * not FULL) and the proposed join must not overlap the LHS.
1201 if (sjinfo->jointype != JOIN_LEFT ||
1202 bms_overlap(joinrelids, sjinfo->min_lefthand))
1203 return false; /* invalid join path */
1206 * To be valid, the proposed join must be a LEFT join; otherwise
1207 * it can't associate into this SJ's RHS. But we may not yet have
1208 * found the SpecialJoinInfo matching the proposed join, so we
1209 * can't test that yet. Remember the requirement for later.
1211 must_be_leftjoin = true;
1216 * Fail if violated any SJ's RHS and didn't match to a LEFT SJ: the
1217 * proposed join can't associate into an SJ's RHS.
1219 * Also, fail if the proposed join's predicate isn't strict; we're
1220 * essentially checking to see if we can apply outer-join identity 3, and
1221 * that's a requirement. (This check may be redundant with checks in
1222 * make_outerjoininfo, but I'm not quite sure, and it's cheap to test.)
1224 if (must_be_leftjoin &&
1225 (match_sjinfo == NULL ||
1226 match_sjinfo->jointype != JOIN_LEFT ||
1227 !match_sjinfo->lhs_strict))
1228 return false; /* invalid join path */
1231 * We also have to check for constraints imposed by LATERAL references.
1233 if (root->hasLateralRTEs)
1237 Relids join_lateral_rels;
1240 * The proposed rels could each contain lateral references to the
1241 * other, in which case the join is impossible. If there are lateral
1242 * references in just one direction, then the join has to be done with
1243 * a nestloop with the lateral referencer on the inside. If the join
1244 * matches an SJ that cannot be implemented by such a nestloop, the
1245 * join is impossible.
1247 * Also, if the lateral reference is only indirect, we should reject
1248 * the join; whatever rel(s) the reference chain goes through must be
1251 * Another case that might keep us from building a valid plan is the
1252 * implementation restriction described by have_dangerous_phv().
1254 lateral_fwd = bms_overlap(rel1->relids, rel2->lateral_relids);
1255 lateral_rev = bms_overlap(rel2->relids, rel1->lateral_relids);
1256 if (lateral_fwd && lateral_rev)
1257 return false; /* have lateral refs in both directions */
1260 /* has to be implemented as nestloop with rel1 on left */
1264 match_sjinfo->jointype == JOIN_FULL))
1265 return false; /* not implementable as nestloop */
1266 /* check there is a direct reference from rel2 to rel1 */
1267 if (!bms_overlap(rel1->relids, rel2->direct_lateral_relids))
1268 return false; /* only indirect refs, so reject */
1269 /* check we won't have a dangerous PHV */
1270 if (have_dangerous_phv(root, rel1->relids, rel2->lateral_relids))
1271 return false; /* might be unable to handle required PHV */
1273 else if (lateral_rev)
1275 /* has to be implemented as nestloop with rel2 on left */
1279 match_sjinfo->jointype == JOIN_FULL))
1280 return false; /* not implementable as nestloop */
1281 /* check there is a direct reference from rel1 to rel2 */
1282 if (!bms_overlap(rel2->relids, rel1->direct_lateral_relids))
1283 return false; /* only indirect refs, so reject */
1284 /* check we won't have a dangerous PHV */
1285 if (have_dangerous_phv(root, rel2->relids, rel1->lateral_relids))
1286 return false; /* might be unable to handle required PHV */
1290 * LATERAL references could also cause problems later on if we accept
1291 * this join: if the join's minimum parameterization includes any rels
1292 * that would have to be on the inside of an outer join with this join
1293 * rel, then it's never going to be possible to build the complete
1294 * query using this join. We should reject this join not only because
1295 * it'll save work, but because if we don't, the clauseless-join
1296 * heuristics might think that legality of this join means that some
1297 * other join rel need not be formed, and that could lead to failure
1298 * to find any plan at all. We have to consider not only rels that
1299 * are directly on the inner side of an OJ with the joinrel, but also
1300 * ones that are indirectly so, so search to find all such rels.
1302 join_lateral_rels = min_join_parameterization(root, joinrelids,
1304 if (join_lateral_rels)
1306 Relids join_plus_rhs = bms_copy(joinrelids);
1312 foreach(l, root->join_info_list)
1314 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1316 /* ignore full joins --- their ordering is predetermined */
1317 if (sjinfo->jointype == JOIN_FULL)
1320 if (bms_overlap(sjinfo->min_lefthand, join_plus_rhs) &&
1321 !bms_is_subset(sjinfo->min_righthand, join_plus_rhs))
1323 join_plus_rhs = bms_add_members(join_plus_rhs,
1324 sjinfo->min_righthand);
1329 if (bms_overlap(join_plus_rhs, join_lateral_rels))
1330 return false; /* will not be able to join to some RHS rel */
1334 /* Otherwise, it's a valid join */
1335 *sjinfo_p = match_sjinfo;
1336 *reversed_p = reversed;
1342 * has_join_restriction
1343 * Detect whether the specified relation has join-order restrictions,
1344 * due to being inside an outer join or an IN (sub-SELECT),
1345 * or participating in any LATERAL references or multi-rel PHVs.
1347 * Essentially, this tests whether have_join_order_restriction() could
1348 * succeed with this rel and some other one. It's OK if we sometimes
1349 * say "true" incorrectly. (Therefore, we don't bother with the relatively
1350 * expensive has_legal_joinclause test.)
1353 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
1357 if (rel->lateral_relids != NULL || rel->lateral_referencers != NULL)
1360 foreach(l, root->placeholder_list)
1362 PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
1364 if (bms_is_subset(rel->relids, phinfo->ph_eval_at) &&
1365 !bms_equal(rel->relids, phinfo->ph_eval_at))
1369 foreach(l, root->join_info_list)
1371 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1373 /* ignore full joins --- other mechanisms preserve their ordering */
1374 if (sjinfo->jointype == JOIN_FULL)
1377 /* ignore if SJ is already contained in rel */
1378 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
1379 bms_is_subset(sjinfo->min_righthand, rel->relids))
1382 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
1383 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
1384 bms_overlap(sjinfo->min_righthand, rel->relids))
1393 * Mark a relation as proven empty.
1395 * During GEQO planning, this can get invoked more than once on the same
1396 * baserel struct, so it's worth checking to see if the rel is already marked
1399 * Also, when called during GEQO join planning, we are in a short-lived
1400 * memory context. We must make sure that the dummy path attached to a
1401 * baserel survives the GEQO cycle, else the baserel is trashed for future
1402 * GEQO cycles. On the other hand, when we are marking a joinrel during GEQO,
1403 * we don't want the dummy path to clutter the main planning context. Upshot
1404 * is that the best solution is to explicitly make the dummy path in the same
1405 * context the given RelOptInfo is in.
1408 mark_dummy_rel(RelOptInfo *rel)
1410 MemoryContext oldcontext;
1412 /* Already marked? */
1413 if (is_dummy_rel(rel))
1416 /* No, so choose correct context to make the dummy path in */
1417 oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
1419 /* Set dummy size estimate */
1422 /* Evict any previously chosen paths */
1423 rel->pathlist = NIL;
1424 rel->partial_pathlist = NIL;
1426 /* Set up the dummy path */
1427 add_path(rel, (Path *) create_append_path(rel, NIL,
1428 rel->lateral_relids,
1431 /* Set or update cheapest_total_path and related fields */
1434 MemoryContextSwitchTo(oldcontext);
1439 * restriction_is_constant_false --- is a restrictlist just false?
1441 * In cases where a qual is provably constant false, eval_const_expressions
1442 * will generally have thrown away anything that's ANDed with it. In outer
1443 * join situations this will leave us computing cartesian products only to
1444 * decide there's no match for an outer row, which is pretty stupid. So,
1445 * we need to detect the case.
1447 * If only_pushed_down is true, then consider only quals that are pushed-down
1448 * from the point of view of the joinrel.
1451 restriction_is_constant_false(List *restrictlist,
1452 RelOptInfo *joinrel,
1453 bool only_pushed_down)
1458 * Despite the above comment, the restriction list we see here might
1459 * possibly have other members besides the FALSE constant, since other
1460 * quals could get "pushed down" to the outer join level. So we check
1461 * each member of the list.
1463 foreach(lc, restrictlist)
1465 RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
1467 if (only_pushed_down && !RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
1470 if (rinfo->clause && IsA(rinfo->clause, Const))
1472 Const *con = (Const *) rinfo->clause;
1474 /* constant NULL is as good as constant FALSE for our purposes */
1475 if (con->constisnull)
1477 if (!DatumGetBool(con->constvalue))