1 /*-------------------------------------------------------------------------
4 * Routines copied from PostgreSQL core distribution.
6 * src/backend/optimizer/path/allpaths.c
7 * set_append_rel_pathlist()
8 * generate_mergeappend_paths()
9 * get_cheapest_parameterized_child_path()
10 * accumulate_append_subpath()
11 * standard_join_search()
13 * src/backend/optimizer/path/joinrels.c
14 * join_search_one_level()
15 * make_rels_by_clause_joins()
16 * make_rels_by_clauseless_joins()
18 * has_join_restriction()
21 * restriction_is_constant_false()
23 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
24 * Portions Copyright (c) 1994, Regents of the University of California
26 *-------------------------------------------------------------------------
30 * set_append_rel_pathlist
31 * Build access paths for an "append relation"
34 set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
35 Index rti, RangeTblEntry *rte)
37 int parentRTindex = rti;
38 List *live_childrels = NIL;
40 bool subpaths_valid = true;
41 List *all_child_pathkeys = NIL;
42 List *all_child_outers = NIL;
46 * Generate access paths for each member relation, and remember the
47 * cheapest path for each one. Also, identify all pathkeys (orderings)
48 * and parameterizations (required_outer sets) available for the member
51 foreach(l, root->append_rel_list)
53 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
55 RangeTblEntry *childRTE;
59 /* append_rel_list contains all append rels; ignore others */
60 if (appinfo->parent_relid != parentRTindex)
63 /* Re-locate the child RTE and RelOptInfo */
64 childRTindex = appinfo->child_relid;
65 childRTE = root->simple_rte_array[childRTindex];
66 childrel = root->simple_rel_array[childRTindex];
69 * Compute the child's access paths.
71 set_rel_pathlist(root, childrel, childRTindex, childRTE);
74 * If child is dummy, ignore it.
76 if (IS_DUMMY_REL(childrel))
80 * Child is live, so add it to the live_childrels list for use below.
82 live_childrels = lappend(live_childrels, childrel);
85 * If child has an unparameterized cheapest-total path, add that to
86 * the unparameterized Append path we are constructing for the parent.
87 * If not, there's no workable unparameterized path.
89 if (childrel->cheapest_total_path->param_info == NULL)
90 subpaths = accumulate_append_subpath(subpaths,
91 childrel->cheapest_total_path);
93 subpaths_valid = false;
96 * Collect lists of all the available path orderings and
97 * parameterizations for all the children. We use these as a
98 * heuristic to indicate which sort orderings and parameterizations we
99 * should build Append and MergeAppend paths for.
101 foreach(lcp, childrel->pathlist)
103 Path *childpath = (Path *) lfirst(lcp);
104 List *childkeys = childpath->pathkeys;
105 Relids childouter = PATH_REQ_OUTER(childpath);
107 /* Unsorted paths don't contribute to pathkey list */
108 if (childkeys != NIL)
113 /* Have we already seen this ordering? */
114 foreach(lpk, all_child_pathkeys)
116 List *existing_pathkeys = (List *) lfirst(lpk);
118 if (compare_pathkeys(existing_pathkeys,
119 childkeys) == PATHKEYS_EQUAL)
127 /* No, so add it to all_child_pathkeys */
128 all_child_pathkeys = lappend(all_child_pathkeys,
133 /* Unparameterized paths don't contribute to param-set list */
139 /* Have we already seen this param set? */
140 foreach(lco, all_child_outers)
142 Relids existing_outers = (Relids) lfirst(lco);
144 if (bms_equal(existing_outers, childouter))
152 /* No, so add it to all_child_outers */
153 all_child_outers = lappend(all_child_outers,
161 * If we found unparameterized paths for all children, build an unordered,
162 * unparameterized Append path for the rel. (Note: this is correct even
163 * if we have zero or one live subpath due to constraint exclusion.)
166 add_path(rel, (Path *) create_append_path(rel, subpaths, NULL));
169 * Also build unparameterized MergeAppend paths based on the collected
170 * list of child pathkeys.
173 generate_mergeappend_paths(root, rel, live_childrels,
177 * Build Append paths for each parameterization seen among the child rels.
178 * (This may look pretty expensive, but in most cases of practical
179 * interest, the child rels will expose mostly the same parameterizations,
180 * so that not that many cases actually get considered here.)
182 * The Append node itself cannot enforce quals, so all qual checking must
183 * be done in the child paths. This means that to have a parameterized
184 * Append path, we must have the exact same parameterization for each
185 * child path; otherwise some children might be failing to check the
186 * moved-down quals. To make them match up, we can try to increase the
187 * parameterization of lesser-parameterized paths.
189 foreach(l, all_child_outers)
191 Relids required_outer = (Relids) lfirst(l);
194 /* Select the child paths for an Append with this parameterization */
196 subpaths_valid = true;
197 foreach(lcr, live_childrels)
199 RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
202 subpath = get_cheapest_parameterized_child_path(root,
207 /* failed to make a suitable path for this child */
208 subpaths_valid = false;
211 subpaths = accumulate_append_subpath(subpaths, subpath);
215 add_path(rel, (Path *)
216 create_append_path(rel, subpaths, required_outer));
219 /* Select cheapest paths */
224 * generate_mergeappend_paths
225 * Generate MergeAppend paths for an append relation
227 * Generate a path for each ordering (pathkey list) appearing in
228 * all_child_pathkeys.
230 * We consider both cheapest-startup and cheapest-total cases, ie, for each
231 * interesting ordering, collect all the cheapest startup subpaths and all the
232 * cheapest total paths, and build a MergeAppend path for each case.
234 * We don't currently generate any parameterized MergeAppend paths. While
235 * it would not take much more code here to do so, it's very unclear that it
236 * is worth the planning cycles to investigate such paths: there's little
237 * use for an ordered path on the inside of a nestloop. In fact, it's likely
238 * that the current coding of add_path would reject such paths out of hand,
239 * because add_path gives no credit for sort ordering of parameterized paths,
240 * and a parameterized MergeAppend is going to be more expensive than the
241 * corresponding parameterized Append path. If we ever try harder to support
242 * parameterized mergejoin plans, it might be worth adding support for
243 * parameterized MergeAppends to feed such joins. (See notes in
244 * optimizer/README for why that might not ever happen, though.)
247 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
248 List *live_childrels,
249 List *all_child_pathkeys)
253 foreach(lcp, all_child_pathkeys)
255 List *pathkeys = (List *) lfirst(lcp);
256 List *startup_subpaths = NIL;
257 List *total_subpaths = NIL;
258 bool startup_neq_total = false;
261 /* Select the child paths for this ordering... */
262 foreach(lcr, live_childrels)
264 RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
265 Path *cheapest_startup,
268 /* Locate the right paths, if they are available. */
270 get_cheapest_path_for_pathkeys(childrel->pathlist,
275 get_cheapest_path_for_pathkeys(childrel->pathlist,
281 * If we can't find any paths with the right order just use the
282 * cheapest-total path; we'll have to sort it later.
284 if (cheapest_startup == NULL || cheapest_total == NULL)
286 cheapest_startup = cheapest_total =
287 childrel->cheapest_total_path;
288 /* Assert we do have an unparameterized path for this child */
289 Assert(cheapest_total->param_info == NULL);
293 * Notice whether we actually have different paths for the
294 * "cheapest" and "total" cases; frequently there will be no point
295 * in two create_merge_append_path() calls.
297 if (cheapest_startup != cheapest_total)
298 startup_neq_total = true;
301 accumulate_append_subpath(startup_subpaths, cheapest_startup);
303 accumulate_append_subpath(total_subpaths, cheapest_total);
306 /* ... and build the MergeAppend paths */
307 add_path(rel, (Path *) create_merge_append_path(root,
312 if (startup_neq_total)
313 add_path(rel, (Path *) create_merge_append_path(root,
322 * get_cheapest_parameterized_child_path
323 * Get cheapest path for this relation that has exactly the requested
326 * Returns NULL if unable to create such a path.
329 get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
330 Relids required_outer)
336 * Look up the cheapest existing path with no more than the needed
337 * parameterization. If it has exactly the needed parameterization, we're
340 cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
344 Assert(cheapest != NULL);
345 if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
349 * Otherwise, we can "reparameterize" an existing path to match the given
350 * parameterization, which effectively means pushing down additional
351 * joinquals to be checked within the path's scan. However, some existing
352 * paths might check the available joinquals already while others don't;
353 * therefore, it's not clear which existing path will be cheapest after
354 * reparameterization. We have to go through them all and find out.
357 foreach(lc, rel->pathlist)
359 Path *path = (Path *) lfirst(lc);
361 /* Can't use it if it needs more than requested parameterization */
362 if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
366 * Reparameterization can only increase the path's cost, so if it's
367 * already more expensive than the current cheapest, forget it.
369 if (cheapest != NULL &&
370 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
373 /* Reparameterize if needed, then recheck cost */
374 if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
376 path = reparameterize_path(root, path, required_outer, 1.0);
378 continue; /* failed to reparameterize this one */
379 Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));
381 if (cheapest != NULL &&
382 compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
386 /* We have a new best path */
390 /* Return the best path, or NULL if we found no suitable candidate */
395 * accumulate_append_subpath
396 * Add a subpath to the list being built for an Append or MergeAppend
398 * It's possible that the child is itself an Append path, in which case
399 * we can "cut out the middleman" and just add its child paths to our
400 * own list. (We don't try to do this earlier because we need to
401 * apply both levels of transformation to the quals.)
404 accumulate_append_subpath(List *subpaths, Path *path)
406 if (IsA(path, AppendPath))
408 AppendPath *apath = (AppendPath *) path;
410 /* list_copy is important here to avoid sharing list substructure */
411 return list_concat(subpaths, list_copy(apath->subpaths));
414 return lappend(subpaths, path);
418 * standard_join_search
419 * Find possible joinpaths for a query by successively finding ways
420 * to join component relations into join relations.
422 * 'levels_needed' is the number of iterations needed, ie, the number of
423 * independent jointree items in the query. This is > 1.
425 * 'initial_rels' is a list of RelOptInfo nodes for each independent
426 * jointree item. These are the components to be joined together.
427 * Note that levels_needed == list_length(initial_rels).
429 * Returns the final level of join relations, i.e., the relation that is
430 * the result of joining all the original relations together.
431 * At least one implementation path must be provided for this relation and
432 * all required sub-relations.
434 * To support loadable plugins that modify planner behavior by changing the
435 * join searching algorithm, we provide a hook variable that lets a plugin
436 * replace or supplement this function. Any such hook must return the same
437 * final join relation as the standard code would, but it might have a
438 * different set of implementation paths attached, and only the sub-joinrels
439 * needed for these paths need have been instantiated.
441 * Note to plugin authors: the functions invoked during standard_join_search()
442 * modify root->join_rel_list and root->join_rel_hash. If you want to do more
443 * than one join-order search, you'll probably need to save and restore the
444 * original states of those data structures. See geqo_eval() for an example.
447 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
453 * This function cannot be invoked recursively within any one planning
454 * problem, so join_rel_level[] can't be in use already.
456 Assert(root->join_rel_level == NULL);
459 * We employ a simple "dynamic programming" algorithm: we first find all
460 * ways to build joins of two jointree items, then all ways to build joins
461 * of three items (from two-item joins and single items), then four-item
462 * joins, and so on until we have considered all ways to join all the
463 * items into one rel.
465 * root->join_rel_level[j] is a list of all the j-item rels. Initially we
466 * set root->join_rel_level[1] to represent all the single-jointree-item
469 root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
471 root->join_rel_level[1] = initial_rels;
473 for (lev = 2; lev <= levels_needed; lev++)
478 * Determine all possible pairs of relations to be joined at this
479 * level, and build paths for making each one from every available
480 * pair of lower-level relations.
482 join_search_one_level(root, lev);
485 * Do cleanup work on each just-processed rel.
487 foreach(lc, root->join_rel_level[lev])
489 rel = (RelOptInfo *) lfirst(lc);
491 /* Find and save the cheapest paths for this rel */
494 #ifdef OPTIMIZER_DEBUG
495 debug_print_rel(root, rel);
501 * We should have a single rel at the final level.
503 if (root->join_rel_level[levels_needed] == NIL)
504 elog(ERROR, "failed to build any %d-way joins", levels_needed);
505 Assert(list_length(root->join_rel_level[levels_needed]) == 1);
507 rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
509 root->join_rel_level = NULL;
515 * join_search_one_level
516 * Consider ways to produce join relations containing exactly 'level'
517 * jointree items. (This is one step of the dynamic-programming method
518 * embodied in standard_join_search.) Join rel nodes for each feasible
519 * combination of lower-level rels are created and returned in a list.
520 * Implementation paths are created for each such joinrel, too.
522 * level: level of rels we want to make this time
523 * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
525 * The result is returned in root->join_rel_level[level].
528 join_search_one_level(PlannerInfo *root, int level)
530 List **joinrels = root->join_rel_level;
534 Assert(joinrels[level] == NIL);
536 /* Set join_cur_level so that new joinrels are added to proper list */
537 root->join_cur_level = level;
540 * First, consider left-sided and right-sided plans, in which rels of
541 * exactly level-1 member relations are joined against initial relations.
542 * We prefer to join using join clauses, but if we find a rel of level-1
543 * members that has no join clauses, we will generate Cartesian-product
544 * joins against all initial rels not already contained in it.
546 foreach(r, joinrels[level - 1])
548 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
550 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
551 has_join_restriction(root, old_rel))
554 * There are join clauses or join order restrictions relevant to
555 * this rel, so consider joins between this rel and (only) those
556 * initial rels it is linked to by a clause or restriction.
558 * At level 2 this condition is symmetric, so there is no need to
559 * look at initial rels before this one in the list; we already
560 * considered such joins when we were at the earlier rel. (The
561 * mirror-image joins are handled automatically by make_join_rel.)
562 * In later passes (level > 2), we join rels of the previous level
563 * to each initial rel they don't already include but have a join
564 * clause or restriction with.
566 ListCell *other_rels;
568 if (level == 2) /* consider remaining initial rels */
569 other_rels = lnext(r);
570 else /* consider all initial rels */
571 other_rels = list_head(joinrels[1]);
573 make_rels_by_clause_joins(root,
580 * Oops, we have a relation that is not joined to any other
581 * relation, either directly or by join-order restrictions.
582 * Cartesian product time.
584 * We consider a cartesian product with each not-already-included
585 * initial rel, whether it has other join clauses or not. At
586 * level 2, if there are two or more clauseless initial rels, we
587 * will redundantly consider joining them in both directions; but
588 * such cases aren't common enough to justify adding complexity to
589 * avoid the duplicated effort.
591 make_rels_by_clauseless_joins(root,
593 list_head(joinrels[1]));
598 * Now, consider "bushy plans" in which relations of k initial rels are
599 * joined to relations of level-k initial rels, for 2 <= k <= level-2.
601 * We only consider bushy-plan joins for pairs of rels where there is a
602 * suitable join clause (or join order restriction), in order to avoid
603 * unreasonable growth of planning time.
607 int other_level = level - k;
610 * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
611 * need to go as far as the halfway point.
616 foreach(r, joinrels[k])
618 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
619 ListCell *other_rels;
623 * We can ignore relations without join clauses here, unless they
624 * participate in join-order restrictions --- then we might have
625 * to force a bushy join plan.
627 if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
628 !has_join_restriction(root, old_rel))
631 if (k == other_level)
632 other_rels = lnext(r); /* only consider remaining rels */
634 other_rels = list_head(joinrels[other_level]);
636 for_each_cell(r2, other_rels)
638 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
640 if (!bms_overlap(old_rel->relids, new_rel->relids))
643 * OK, we can build a rel of the right level from this
644 * pair of rels. Do so if there is at least one relevant
645 * join clause or join order restriction.
647 if (have_relevant_joinclause(root, old_rel, new_rel) ||
648 have_join_order_restriction(root, old_rel, new_rel))
650 (void) make_join_rel(root, old_rel, new_rel);
658 * Last-ditch effort: if we failed to find any usable joins so far, force
659 * a set of cartesian-product joins to be generated. This handles the
660 * special case where all the available rels have join clauses but we
661 * cannot use any of those clauses yet. This can only happen when we are
662 * considering a join sub-problem (a sub-joinlist) and all the rels in the
663 * sub-problem have only join clauses with rels outside the sub-problem.
666 * SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
667 * WHERE a.w = c.x and b.y = d.z;
669 * If the "a INNER JOIN b" sub-problem does not get flattened into the
670 * upper level, we must be willing to make a cartesian join of a and b;
671 * but the code above will not have done so, because it thought that both
672 * a and b have joinclauses. We consider only left-sided and right-sided
673 * cartesian joins in this case (no bushy).
676 if (joinrels[level] == NIL)
679 * This loop is just like the first one, except we always call
680 * make_rels_by_clauseless_joins().
682 foreach(r, joinrels[level - 1])
684 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
686 make_rels_by_clauseless_joins(root,
688 list_head(joinrels[1]));
692 * When special joins are involved, there may be no legal way
693 * to make an N-way join for some values of N. For example consider
695 * SELECT ... FROM t1 WHERE
696 * x IN (SELECT ... FROM t2,t3 WHERE ...) AND
697 * y IN (SELECT ... FROM t4,t5 WHERE ...)
699 * We will flatten this query to a 5-way join problem, but there are
700 * no 4-way joins that join_is_legal() will consider legal. We have
701 * to accept failure at level 4 and go on to discover a workable
702 * bushy plan at level 5.
704 * However, if there are no special joins and no lateral references
705 * then join_is_legal() should never fail, and so the following sanity
709 if (joinrels[level] == NIL &&
710 root->join_info_list == NIL &&
711 root->lateral_info_list == NIL)
712 elog(ERROR, "failed to build any %d-way joins", level);
717 * make_rels_by_clause_joins
718 * Build joins between the given relation 'old_rel' and other relations
719 * that participate in join clauses that 'old_rel' also participates in
720 * (or participate in join-order restrictions with it).
721 * The join rels are returned in root->join_rel_level[join_cur_level].
723 * Note: at levels above 2 we will generate the same joined relation in
724 * multiple ways --- for example (a join b) join c is the same RelOptInfo as
725 * (b join c) join a, though the second case will add a different set of Paths
726 * to it. This is the reason for using the join_rel_level mechanism, which
727 * automatically ensures that each new joinrel is only added to the list once.
729 * 'old_rel' is the relation entry for the relation to be joined
730 * 'other_rels': the first cell in a linked list containing the other
731 * rels to be considered for joining
733 * Currently, this is only used with initial rels in other_rels, but it
734 * will work for joining to joinrels too.
737 make_rels_by_clause_joins(PlannerInfo *root,
739 ListCell *other_rels)
743 for_each_cell(l, other_rels)
745 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
747 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
748 (have_relevant_joinclause(root, old_rel, other_rel) ||
749 have_join_order_restriction(root, old_rel, other_rel)))
751 (void) make_join_rel(root, old_rel, other_rel);
757 * make_rels_by_clauseless_joins
758 * Given a relation 'old_rel' and a list of other relations
759 * 'other_rels', create a join relation between 'old_rel' and each
760 * member of 'other_rels' that isn't already included in 'old_rel'.
761 * The join rels are returned in root->join_rel_level[join_cur_level].
763 * 'old_rel' is the relation entry for the relation to be joined
764 * 'other_rels': the first cell of a linked list containing the
765 * other rels to be considered for joining
767 * Currently, this is only used with initial rels in other_rels, but it would
768 * work for joining to joinrels too.
771 make_rels_by_clauseless_joins(PlannerInfo *root,
773 ListCell *other_rels)
777 for_each_cell(l, other_rels)
779 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
781 if (!bms_overlap(other_rel->relids, old_rel->relids))
783 (void) make_join_rel(root, old_rel, other_rel);
790 * Determine whether a proposed join is legal given the query's
791 * join order constraints; and if it is, determine the join type.
793 * Caller must supply not only the two rels, but the union of their relids.
794 * (We could simplify the API by computing joinrelids locally, but this
795 * would be redundant work in the normal path through make_join_rel.)
797 * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
798 * else it's set to point to the associated SpecialJoinInfo node. Also,
799 * *reversed_p is set TRUE if the given relations need to be swapped to
800 * match the SpecialJoinInfo node.
803 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
805 SpecialJoinInfo **sjinfo_p, bool *reversed_p)
807 SpecialJoinInfo *match_sjinfo;
816 * Ensure output params are set on failure return. This is just to
817 * suppress uninitialized-variable warnings from overly anal compilers.
823 * If we have any special joins, the proposed join might be illegal; and
824 * in any case we have to determine its join type. Scan the join info
825 * list for conflicts.
829 unique_ified = false;
830 is_valid_inner = true;
832 foreach(l, root->join_info_list)
834 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
837 * This special join is not relevant unless its RHS overlaps the
838 * proposed join. (Check this first as a fast path for dismissing
839 * most irrelevant SJs quickly.)
841 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
845 * Also, not relevant if proposed join is fully contained within RHS
846 * (ie, we're still building up the RHS).
848 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
852 * Also, not relevant if SJ is already done within either input.
854 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
855 bms_is_subset(sjinfo->min_righthand, rel1->relids))
857 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
858 bms_is_subset(sjinfo->min_righthand, rel2->relids))
862 * If it's a semijoin and we already joined the RHS to any other rels
863 * within either input, then we must have unique-ified the RHS at that
864 * point (see below). Therefore the semijoin is no longer relevant in
867 if (sjinfo->jointype == JOIN_SEMI)
869 if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
870 !bms_equal(sjinfo->syn_righthand, rel1->relids))
872 if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
873 !bms_equal(sjinfo->syn_righthand, rel2->relids))
878 * If one input contains min_lefthand and the other contains
879 * min_righthand, then we can perform the SJ at this join.
881 * Barf if we get matches to more than one SJ (is that possible?)
883 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
884 bms_is_subset(sjinfo->min_righthand, rel2->relids))
887 return false; /* invalid join path */
888 match_sjinfo = sjinfo;
891 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
892 bms_is_subset(sjinfo->min_righthand, rel1->relids))
895 return false; /* invalid join path */
896 match_sjinfo = sjinfo;
899 else if (sjinfo->jointype == JOIN_SEMI &&
900 bms_equal(sjinfo->syn_righthand, rel2->relids) &&
901 create_unique_path(root, rel2, rel2->cheapest_total_path,
905 * For a semijoin, we can join the RHS to anything else by
906 * unique-ifying the RHS (if the RHS can be unique-ified).
907 * We will only get here if we have the full RHS but less
908 * than min_lefthand on the LHS.
910 * The reason to consider such a join path is exemplified by
911 * SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
912 * If we insist on doing this as a semijoin we will first have
913 * to form the cartesian product of A*B. But if we unique-ify
914 * C then the semijoin becomes a plain innerjoin and we can join
915 * in any order, eg C to A and then to B. When C is much smaller
916 * than A and B this can be a huge win. So we allow C to be
917 * joined to just A or just B here, and then make_join_rel has
918 * to handle the case properly.
920 * Note that actually we'll allow unique-ified C to be joined to
921 * some other relation D here, too. That is legal, if usually not
922 * very sane, and this routine is only concerned with legality not
923 * with whether the join is good strategy.
927 return false; /* invalid join path */
928 match_sjinfo = sjinfo;
932 else if (sjinfo->jointype == JOIN_SEMI &&
933 bms_equal(sjinfo->syn_righthand, rel1->relids) &&
934 create_unique_path(root, rel1, rel1->cheapest_total_path,
937 /* Reversed semijoin case */
939 return false; /* invalid join path */
940 match_sjinfo = sjinfo;
947 * Otherwise, the proposed join overlaps the RHS but isn't
948 * a valid implementation of this SJ. It might still be
949 * a legal join, however. If both inputs overlap the RHS,
950 * assume that it's OK. Since the inputs presumably got past
951 * this function's checks previously, they can't overlap the
952 * LHS and their violations of the RHS boundary must represent
953 * SJs that have been determined to commute with this one.
954 * We have to allow this to work correctly in cases like
955 * (a LEFT JOIN (b JOIN (c LEFT JOIN d)))
956 * when the c/d join has been determined to commute with the join
957 * to a, and hence d is not part of min_righthand for the upper
958 * join. It should be legal to join b to c/d but this will appear
959 * as a violation of the upper join's RHS.
960 * Furthermore, if one input overlaps the RHS and the other does
961 * not, we should still allow the join if it is a valid
962 * implementation of some other SJ. We have to allow this to
963 * support the associative identity
964 * (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab
965 * since joining B directly to C violates the lower SJ's RHS.
966 * We assume that make_outerjoininfo() set things up correctly
967 * so that we'll only match to some SJ if the join is valid.
968 * Set flag here to check at bottom of loop.
971 if (sjinfo->jointype != JOIN_SEMI &&
972 bms_overlap(rel1->relids, sjinfo->min_righthand) &&
973 bms_overlap(rel2->relids, sjinfo->min_righthand))
976 Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand));
979 is_valid_inner = false;
984 * Fail if violated some SJ's RHS and didn't match to another SJ. However,
985 * "matching" to a semijoin we are implementing by unique-ification
986 * doesn't count (think: it's really an inner join).
988 if (!is_valid_inner &&
989 (match_sjinfo == NULL || unique_ified))
990 return false; /* invalid join path */
993 * We also have to check for constraints imposed by LATERAL references.
994 * The proposed rels could each contain lateral references to the other,
995 * in which case the join is impossible. If there are lateral references
996 * in just one direction, then the join has to be done with a nestloop
997 * with the lateral referencer on the inside. If the join matches an SJ
998 * that cannot be implemented by such a nestloop, the join is impossible.
1000 lateral_fwd = lateral_rev = false;
1001 foreach(l, root->lateral_info_list)
1003 LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
1005 if (bms_is_subset(ljinfo->lateral_rhs, rel2->relids) &&
1006 bms_overlap(ljinfo->lateral_lhs, rel1->relids))
1008 /* has to be implemented as nestloop with rel1 on left */
1010 return false; /* have lateral refs in both directions */
1012 if (!bms_is_subset(ljinfo->lateral_lhs, rel1->relids))
1013 return false; /* rel1 can't compute the required parameter */
1015 (reversed || match_sjinfo->jointype == JOIN_FULL))
1016 return false; /* not implementable as nestloop */
1018 if (bms_is_subset(ljinfo->lateral_rhs, rel1->relids) &&
1019 bms_overlap(ljinfo->lateral_lhs, rel2->relids))
1021 /* has to be implemented as nestloop with rel2 on left */
1023 return false; /* have lateral refs in both directions */
1025 if (!bms_is_subset(ljinfo->lateral_lhs, rel2->relids))
1026 return false; /* rel2 can't compute the required parameter */
1028 (!reversed || match_sjinfo->jointype == JOIN_FULL))
1029 return false; /* not implementable as nestloop */
1033 /* Otherwise, it's a valid join */
1034 *sjinfo_p = match_sjinfo;
1035 *reversed_p = reversed;
1040 * has_join_restriction
1041 * Detect whether the specified relation has join-order restrictions,
1042 * due to being inside an outer join or an IN (sub-SELECT),
1043 * or participating in any LATERAL references.
1045 * Essentially, this tests whether have_join_order_restriction() could
1046 * succeed with this rel and some other one. It's OK if we sometimes
1047 * say "true" incorrectly. (Therefore, we don't bother with the relatively
1048 * expensive has_legal_joinclause test.)
1051 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
1055 foreach(l, root->lateral_info_list)
1057 LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
1059 if (bms_is_subset(ljinfo->lateral_rhs, rel->relids) ||
1060 bms_overlap(ljinfo->lateral_lhs, rel->relids))
1064 foreach(l, root->join_info_list)
1066 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
1068 /* ignore full joins --- other mechanisms preserve their ordering */
1069 if (sjinfo->jointype == JOIN_FULL)
1072 /* ignore if SJ is already contained in rel */
1073 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
1074 bms_is_subset(sjinfo->min_righthand, rel->relids))
1077 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
1078 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
1079 bms_overlap(sjinfo->min_righthand, rel->relids))
1087 * is_dummy_rel --- has relation been proven empty?
1090 is_dummy_rel(RelOptInfo *rel)
1092 return IS_DUMMY_REL(rel);
1096 * Mark a relation as proven empty.
1098 * During GEQO planning, this can get invoked more than once on the same
1099 * baserel struct, so it's worth checking to see if the rel is already marked
1102 * Also, when called during GEQO join planning, we are in a short-lived
1103 * memory context. We must make sure that the dummy path attached to a
1104 * baserel survives the GEQO cycle, else the baserel is trashed for future
1105 * GEQO cycles. On the other hand, when we are marking a joinrel during GEQO,
1106 * we don't want the dummy path to clutter the main planning context. Upshot
1107 * is that the best solution is to explicitly make the dummy path in the same
1108 * context the given RelOptInfo is in.
1111 mark_dummy_rel(RelOptInfo *rel)
1113 MemoryContext oldcontext;
1115 /* Already marked? */
1116 if (is_dummy_rel(rel))
1119 /* No, so choose correct context to make the dummy path in */
1120 oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
1122 /* Set dummy size estimate */
1125 /* Evict any previously chosen paths */
1126 rel->pathlist = NIL;
1128 /* Set up the dummy path */
1129 add_path(rel, (Path *) create_append_path(rel, NIL, NULL));
1131 /* Set or update cheapest_total_path and related fields */
1134 MemoryContextSwitchTo(oldcontext);
1138 * restriction_is_constant_false --- is a restrictlist just FALSE?
1140 * In cases where a qual is provably constant FALSE, eval_const_expressions
1141 * will generally have thrown away anything that's ANDed with it. In outer
1142 * join situations this will leave us computing cartesian products only to
1143 * decide there's no match for an outer row, which is pretty stupid. So,
1144 * we need to detect the case.
1146 * If only_pushed_down is TRUE, then consider only pushed-down quals.
1149 restriction_is_constant_false(List *restrictlist, bool only_pushed_down)
1154 * Despite the above comment, the restriction list we see here might
1155 * possibly have other members besides the FALSE constant, since other
1156 * quals could get "pushed down" to the outer join level. So we check
1157 * each member of the list.
1159 foreach(lc, restrictlist)
1161 RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
1163 Assert(IsA(rinfo, RestrictInfo));
1164 if (only_pushed_down && !rinfo->is_pushed_down)
1167 if (rinfo->clause && IsA(rinfo->clause, Const))
1169 Const *con = (Const *) rinfo->clause;
1171 /* constant NULL is as good as constant FALSE for our purposes */
1172 if (con->constisnull)
1174 if (!DatumGetBool(con->constvalue))