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 * accumulate_append_subpath()
10 * standard_join_search()
12 * src/backend/optimizer/path/joinrels.c
13 * join_search_one_level()
14 * make_rels_by_clause_joins()
15 * make_rels_by_clauseless_joins()
17 * has_join_restriction()
20 * restriction_is_constant_false()
22 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
23 * Portions Copyright (c) 1994, Regents of the University of California
25 *-------------------------------------------------------------------------
29 * set_append_rel_pathlist
30 * Build access paths for an "append relation"
33 set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
34 Index rti, RangeTblEntry *rte)
36 int parentRTindex = rti;
37 List *live_childrels = NIL;
39 List *all_child_pathkeys = NIL;
40 List *all_child_outers = NIL;
44 * Generate access paths for each member relation, and remember the
45 * cheapest path for each one. Also, identify all pathkeys (orderings)
46 * and parameterizations (required_outer sets) available for the member
49 foreach(l, root->append_rel_list)
51 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
53 RangeTblEntry *childRTE;
57 /* append_rel_list contains all append rels; ignore others */
58 if (appinfo->parent_relid != parentRTindex)
61 /* Re-locate the child RTE and RelOptInfo */
62 childRTindex = appinfo->child_relid;
63 childRTE = root->simple_rte_array[childRTindex];
64 childrel = root->simple_rel_array[childRTindex];
67 * Compute the child's access paths.
69 set_rel_pathlist(root, childrel, childRTindex, childRTE);
72 * If child is dummy, ignore it.
74 if (IS_DUMMY_REL(childrel))
78 * Child is live, so add its cheapest access path to the Append path
79 * we are constructing for the parent.
81 subpaths = accumulate_append_subpath(subpaths,
82 childrel->cheapest_total_path);
84 /* Remember which childrels are live, for logic below */
85 live_childrels = lappend(live_childrels, childrel);
88 * Collect lists of all the available path orderings and
89 * parameterizations for all the children. We use these as a
90 * heuristic to indicate which sort orderings and parameterizations we
91 * should build Append and MergeAppend paths for.
93 foreach(lcp, childrel->pathlist)
95 Path *childpath = (Path *) lfirst(lcp);
96 List *childkeys = childpath->pathkeys;
97 Relids childouter = PATH_REQ_OUTER(childpath);
99 /* Unsorted paths don't contribute to pathkey list */
100 if (childkeys != NIL)
105 /* Have we already seen this ordering? */
106 foreach(lpk, all_child_pathkeys)
108 List *existing_pathkeys = (List *) lfirst(lpk);
110 if (compare_pathkeys(existing_pathkeys,
111 childkeys) == PATHKEYS_EQUAL)
119 /* No, so add it to all_child_pathkeys */
120 all_child_pathkeys = lappend(all_child_pathkeys,
125 /* Unparameterized paths don't contribute to param-set list */
131 /* Have we already seen this param set? */
132 foreach(lco, all_child_outers)
134 Relids existing_outers = (Relids) lfirst(lco);
136 if (bms_equal(existing_outers, childouter))
144 /* No, so add it to all_child_outers */
145 all_child_outers = lappend(all_child_outers,
153 * Next, build an unordered, unparameterized Append path for the rel.
154 * (Note: this is correct even if we have zero or one live subpath due to
155 * constraint exclusion.)
157 add_path(rel, (Path *) create_append_path(rel, subpaths, NULL));
160 * Build unparameterized MergeAppend paths based on the collected list of
163 generate_mergeappend_paths(root, rel, live_childrels, all_child_pathkeys);
166 * Build Append paths for each parameterization seen among the child rels.
167 * (This may look pretty expensive, but in most cases of practical
168 * interest, the child rels will expose mostly the same parameterizations,
169 * so that not that many cases actually get considered here.)
171 * The Append node itself cannot enforce quals, so all qual checking must
172 * be done in the child paths. This means that to have a parameterized
173 * Append path, we must have the exact same parameterization for each
174 * child path; otherwise some children might be failing to check the
175 * moved-down quals. To make them match up, we can try to increase the
176 * parameterization of lesser-parameterized paths.
178 foreach(l, all_child_outers)
180 Relids required_outer = (Relids) lfirst(l);
184 /* Select the child paths for an Append with this parameterization */
186 foreach(lcr, live_childrels)
188 RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
189 Path *cheapest_total;
192 get_cheapest_path_for_pathkeys(childrel->pathlist,
196 Assert(cheapest_total != NULL);
198 /* Children must have exactly the desired parameterization */
199 if (!bms_equal(PATH_REQ_OUTER(cheapest_total), required_outer))
201 cheapest_total = reparameterize_path(root, cheapest_total,
202 required_outer, 1.0);
203 if (cheapest_total == NULL)
210 subpaths = accumulate_append_subpath(subpaths, cheapest_total);
214 add_path(rel, (Path *)
215 create_append_path(rel, subpaths, required_outer));
218 /* Select cheapest paths */
223 * generate_mergeappend_paths
224 * Generate MergeAppend paths for an append relation
226 * Generate a path for each ordering (pathkey list) appearing in
227 * all_child_pathkeys.
229 * We consider both cheapest-startup and cheapest-total cases, ie, for each
230 * interesting ordering, collect all the cheapest startup subpaths and all the
231 * cheapest total paths, and build a MergeAppend path for each case.
233 * We don't currently generate any parameterized MergeAppend paths. While
234 * it would not take much more code here to do so, it's very unclear that it
235 * is worth the planning cycles to investigate such paths: there's little
236 * use for an ordered path on the inside of a nestloop. In fact, it's likely
237 * that the current coding of add_path would reject such paths out of hand,
238 * because add_path gives no credit for sort ordering of parameterized paths,
239 * and a parameterized MergeAppend is going to be more expensive than the
240 * corresponding parameterized Append path. If we ever try harder to support
241 * parameterized mergejoin plans, it might be worth adding support for
242 * parameterized MergeAppends to feed such joins. (See notes in
243 * optimizer/README for why that might not ever happen, though.)
246 generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
247 List *live_childrels,
248 List *all_child_pathkeys)
252 foreach(lcp, all_child_pathkeys)
254 List *pathkeys = (List *) lfirst(lcp);
255 List *startup_subpaths = NIL;
256 List *total_subpaths = NIL;
257 bool startup_neq_total = false;
260 /* Select the child paths for this ordering... */
261 foreach(lcr, live_childrels)
263 RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
264 Path *cheapest_startup,
267 /* Locate the right paths, if they are available. */
269 get_cheapest_path_for_pathkeys(childrel->pathlist,
274 get_cheapest_path_for_pathkeys(childrel->pathlist,
280 * If we can't find any paths with the right order just use the
281 * cheapest-total path; we'll have to sort it later.
283 if (cheapest_startup == NULL || cheapest_total == NULL)
285 cheapest_startup = cheapest_total =
286 childrel->cheapest_total_path;
287 Assert(cheapest_total != NULL);
291 * Notice whether we actually have different paths for the
292 * "cheapest" and "total" cases; frequently there will be no point
293 * in two create_merge_append_path() calls.
295 if (cheapest_startup != cheapest_total)
296 startup_neq_total = true;
299 accumulate_append_subpath(startup_subpaths, cheapest_startup);
301 accumulate_append_subpath(total_subpaths, cheapest_total);
304 /* ... and build the MergeAppend paths */
305 add_path(rel, (Path *) create_merge_append_path(root,
310 if (startup_neq_total)
311 add_path(rel, (Path *) create_merge_append_path(root,
320 * accumulate_append_subpath
321 * Add a subpath to the list being built for an Append or MergeAppend
323 * It's possible that the child is itself an Append path, in which case
324 * we can "cut out the middleman" and just add its child paths to our
325 * own list. (We don't try to do this earlier because we need to
326 * apply both levels of transformation to the quals.)
329 accumulate_append_subpath(List *subpaths, Path *path)
331 if (IsA(path, AppendPath))
333 AppendPath *apath = (AppendPath *) path;
335 /* list_copy is important here to avoid sharing list substructure */
336 return list_concat(subpaths, list_copy(apath->subpaths));
339 return lappend(subpaths, path);
343 * standard_join_search
344 * Find possible joinpaths for a query by successively finding ways
345 * to join component relations into join relations.
347 * 'levels_needed' is the number of iterations needed, ie, the number of
348 * independent jointree items in the query. This is > 1.
350 * 'initial_rels' is a list of RelOptInfo nodes for each independent
351 * jointree item. These are the components to be joined together.
352 * Note that levels_needed == list_length(initial_rels).
354 * Returns the final level of join relations, i.e., the relation that is
355 * the result of joining all the original relations together.
356 * At least one implementation path must be provided for this relation and
357 * all required sub-relations.
359 * To support loadable plugins that modify planner behavior by changing the
360 * join searching algorithm, we provide a hook variable that lets a plugin
361 * replace or supplement this function. Any such hook must return the same
362 * final join relation as the standard code would, but it might have a
363 * different set of implementation paths attached, and only the sub-joinrels
364 * needed for these paths need have been instantiated.
366 * Note to plugin authors: the functions invoked during standard_join_search()
367 * modify root->join_rel_list and root->join_rel_hash. If you want to do more
368 * than one join-order search, you'll probably need to save and restore the
369 * original states of those data structures. See geqo_eval() for an example.
372 standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
378 * This function cannot be invoked recursively within any one planning
379 * problem, so join_rel_level[] can't be in use already.
381 Assert(root->join_rel_level == NULL);
384 * We employ a simple "dynamic programming" algorithm: we first find all
385 * ways to build joins of two jointree items, then all ways to build joins
386 * of three items (from two-item joins and single items), then four-item
387 * joins, and so on until we have considered all ways to join all the
388 * items into one rel.
390 * root->join_rel_level[j] is a list of all the j-item rels. Initially we
391 * set root->join_rel_level[1] to represent all the single-jointree-item
394 root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));
396 root->join_rel_level[1] = initial_rels;
398 for (lev = 2; lev <= levels_needed; lev++)
403 * Determine all possible pairs of relations to be joined at this
404 * level, and build paths for making each one from every available
405 * pair of lower-level relations.
407 join_search_one_level(root, lev);
410 * Do cleanup work on each just-processed rel.
412 foreach(lc, root->join_rel_level[lev])
414 rel = (RelOptInfo *) lfirst(lc);
416 /* Find and save the cheapest paths for this rel */
419 #ifdef OPTIMIZER_DEBUG
420 debug_print_rel(root, rel);
426 * We should have a single rel at the final level.
428 if (root->join_rel_level[levels_needed] == NIL)
429 elog(ERROR, "failed to build any %d-way joins", levels_needed);
430 Assert(list_length(root->join_rel_level[levels_needed]) == 1);
432 rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);
434 root->join_rel_level = NULL;
440 * join_search_one_level
441 * Consider ways to produce join relations containing exactly 'level'
442 * jointree items. (This is one step of the dynamic-programming method
443 * embodied in standard_join_search.) Join rel nodes for each feasible
444 * combination of lower-level rels are created and returned in a list.
445 * Implementation paths are created for each such joinrel, too.
447 * level: level of rels we want to make this time
448 * root->join_rel_level[j], 1 <= j < level, is a list of rels containing j items
450 * The result is returned in root->join_rel_level[level].
453 join_search_one_level(PlannerInfo *root, int level)
455 List **joinrels = root->join_rel_level;
459 Assert(joinrels[level] == NIL);
461 /* Set join_cur_level so that new joinrels are added to proper list */
462 root->join_cur_level = level;
465 * First, consider left-sided and right-sided plans, in which rels of
466 * exactly level-1 member relations are joined against initial relations.
467 * We prefer to join using join clauses, but if we find a rel of level-1
468 * members that has no join clauses, we will generate Cartesian-product
469 * joins against all initial rels not already contained in it.
471 foreach(r, joinrels[level - 1])
473 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
475 if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
476 has_join_restriction(root, old_rel))
479 * There are join clauses or join order restrictions relevant to
480 * this rel, so consider joins between this rel and (only) those
481 * initial rels it is linked to by a clause or restriction.
483 * At level 2 this condition is symmetric, so there is no need to
484 * look at initial rels before this one in the list; we already
485 * considered such joins when we were at the earlier rel. (The
486 * mirror-image joins are handled automatically by make_join_rel.)
487 * In later passes (level > 2), we join rels of the previous level
488 * to each initial rel they don't already include but have a join
489 * clause or restriction with.
491 ListCell *other_rels;
493 if (level == 2) /* consider remaining initial rels */
494 other_rels = lnext(r);
495 else /* consider all initial rels */
496 other_rels = list_head(joinrels[1]);
498 make_rels_by_clause_joins(root,
505 * Oops, we have a relation that is not joined to any other
506 * relation, either directly or by join-order restrictions.
507 * Cartesian product time.
509 * We consider a cartesian product with each not-already-included
510 * initial rel, whether it has other join clauses or not. At
511 * level 2, if there are two or more clauseless initial rels, we
512 * will redundantly consider joining them in both directions; but
513 * such cases aren't common enough to justify adding complexity to
514 * avoid the duplicated effort.
516 make_rels_by_clauseless_joins(root,
518 list_head(joinrels[1]));
523 * Now, consider "bushy plans" in which relations of k initial rels are
524 * joined to relations of level-k initial rels, for 2 <= k <= level-2.
526 * We only consider bushy-plan joins for pairs of rels where there is a
527 * suitable join clause (or join order restriction), in order to avoid
528 * unreasonable growth of planning time.
532 int other_level = level - k;
535 * Since make_join_rel(x, y) handles both x,y and y,x cases, we only
536 * need to go as far as the halfway point.
541 foreach(r, joinrels[k])
543 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
544 ListCell *other_rels;
548 * We can ignore relations without join clauses here, unless they
549 * participate in join-order restrictions --- then we might have
550 * to force a bushy join plan.
552 if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
553 !has_join_restriction(root, old_rel))
556 if (k == other_level)
557 other_rels = lnext(r); /* only consider remaining rels */
559 other_rels = list_head(joinrels[other_level]);
561 for_each_cell(r2, other_rels)
563 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
565 if (!bms_overlap(old_rel->relids, new_rel->relids))
568 * OK, we can build a rel of the right level from this
569 * pair of rels. Do so if there is at least one relevant
570 * join clause or join order restriction.
572 if (have_relevant_joinclause(root, old_rel, new_rel) ||
573 have_join_order_restriction(root, old_rel, new_rel))
575 (void) make_join_rel(root, old_rel, new_rel);
583 * Last-ditch effort: if we failed to find any usable joins so far, force
584 * a set of cartesian-product joins to be generated. This handles the
585 * special case where all the available rels have join clauses but we
586 * cannot use any of those clauses yet. This can only happen when we are
587 * considering a join sub-problem (a sub-joinlist) and all the rels in the
588 * sub-problem have only join clauses with rels outside the sub-problem.
591 * SELECT ... FROM a INNER JOIN b ON TRUE, c, d, ...
592 * WHERE a.w = c.x and b.y = d.z;
594 * If the "a INNER JOIN b" sub-problem does not get flattened into the
595 * upper level, we must be willing to make a cartesian join of a and b;
596 * but the code above will not have done so, because it thought that both
597 * a and b have joinclauses. We consider only left-sided and right-sided
598 * cartesian joins in this case (no bushy).
601 if (joinrels[level] == NIL)
604 * This loop is just like the first one, except we always call
605 * make_rels_by_clauseless_joins().
607 foreach(r, joinrels[level - 1])
609 RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
611 make_rels_by_clauseless_joins(root,
613 list_head(joinrels[1]));
617 * When special joins are involved, there may be no legal way
618 * to make an N-way join for some values of N. For example consider
620 * SELECT ... FROM t1 WHERE
621 * x IN (SELECT ... FROM t2,t3 WHERE ...) AND
622 * y IN (SELECT ... FROM t4,t5 WHERE ...)
624 * We will flatten this query to a 5-way join problem, but there are
625 * no 4-way joins that join_is_legal() will consider legal. We have
626 * to accept failure at level 4 and go on to discover a workable
627 * bushy plan at level 5.
629 * However, if there are no special joins then join_is_legal() should
630 * never fail, and so the following sanity check is useful.
633 if (joinrels[level] == NIL && root->join_info_list == NIL)
634 elog(ERROR, "failed to build any %d-way joins", level);
639 * make_rels_by_clause_joins
640 * Build joins between the given relation 'old_rel' and other relations
641 * that participate in join clauses that 'old_rel' also participates in
642 * (or participate in join-order restrictions with it).
643 * The join rels are returned in root->join_rel_level[join_cur_level].
645 * Note: at levels above 2 we will generate the same joined relation in
646 * multiple ways --- for example (a join b) join c is the same RelOptInfo as
647 * (b join c) join a, though the second case will add a different set of Paths
648 * to it. This is the reason for using the join_rel_level mechanism, which
649 * automatically ensures that each new joinrel is only added to the list once.
651 * 'old_rel' is the relation entry for the relation to be joined
652 * 'other_rels': the first cell in a linked list containing the other
653 * rels to be considered for joining
655 * Currently, this is only used with initial rels in other_rels, but it
656 * will work for joining to joinrels too.
659 make_rels_by_clause_joins(PlannerInfo *root,
661 ListCell *other_rels)
665 for_each_cell(l, other_rels)
667 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
669 if (!bms_overlap(old_rel->relids, other_rel->relids) &&
670 (have_relevant_joinclause(root, old_rel, other_rel) ||
671 have_join_order_restriction(root, old_rel, other_rel)))
673 (void) make_join_rel(root, old_rel, other_rel);
679 * make_rels_by_clauseless_joins
680 * Given a relation 'old_rel' and a list of other relations
681 * 'other_rels', create a join relation between 'old_rel' and each
682 * member of 'other_rels' that isn't already included in 'old_rel'.
683 * The join rels are returned in root->join_rel_level[join_cur_level].
685 * 'old_rel' is the relation entry for the relation to be joined
686 * 'other_rels': the first cell of a linked list containing the
687 * other rels to be considered for joining
689 * Currently, this is only used with initial rels in other_rels, but it would
690 * work for joining to joinrels too.
693 make_rels_by_clauseless_joins(PlannerInfo *root,
695 ListCell *other_rels)
699 for_each_cell(l, other_rels)
701 RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
703 if (!bms_overlap(other_rel->relids, old_rel->relids))
705 (void) make_join_rel(root, old_rel, other_rel);
712 * Determine whether a proposed join is legal given the query's
713 * join order constraints; and if it is, determine the join type.
715 * Caller must supply not only the two rels, but the union of their relids.
716 * (We could simplify the API by computing joinrelids locally, but this
717 * would be redundant work in the normal path through make_join_rel.)
719 * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
720 * else it's set to point to the associated SpecialJoinInfo node. Also,
721 * *reversed_p is set TRUE if the given relations need to be swapped to
722 * match the SpecialJoinInfo node.
725 join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
727 SpecialJoinInfo **sjinfo_p, bool *reversed_p)
729 SpecialJoinInfo *match_sjinfo;
736 * Ensure output params are set on failure return. This is just to
737 * suppress uninitialized-variable warnings from overly anal compilers.
743 * If we have any special joins, the proposed join might be illegal; and
744 * in any case we have to determine its join type. Scan the join info
745 * list for conflicts.
749 unique_ified = false;
750 is_valid_inner = true;
752 foreach(l, root->join_info_list)
754 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
757 * This special join is not relevant unless its RHS overlaps the
758 * proposed join. (Check this first as a fast path for dismissing
759 * most irrelevant SJs quickly.)
761 if (!bms_overlap(sjinfo->min_righthand, joinrelids))
765 * Also, not relevant if proposed join is fully contained within RHS
766 * (ie, we're still building up the RHS).
768 if (bms_is_subset(joinrelids, sjinfo->min_righthand))
772 * Also, not relevant if SJ is already done within either input.
774 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
775 bms_is_subset(sjinfo->min_righthand, rel1->relids))
777 if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
778 bms_is_subset(sjinfo->min_righthand, rel2->relids))
782 * If it's a semijoin and we already joined the RHS to any other rels
783 * within either input, then we must have unique-ified the RHS at that
784 * point (see below). Therefore the semijoin is no longer relevant in
787 if (sjinfo->jointype == JOIN_SEMI)
789 if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
790 !bms_equal(sjinfo->syn_righthand, rel1->relids))
792 if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
793 !bms_equal(sjinfo->syn_righthand, rel2->relids))
798 * If one input contains min_lefthand and the other contains
799 * min_righthand, then we can perform the SJ at this join.
801 * Barf if we get matches to more than one SJ (is that possible?)
803 if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
804 bms_is_subset(sjinfo->min_righthand, rel2->relids))
807 return false; /* invalid join path */
808 match_sjinfo = sjinfo;
811 else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
812 bms_is_subset(sjinfo->min_righthand, rel1->relids))
815 return false; /* invalid join path */
816 match_sjinfo = sjinfo;
819 else if (sjinfo->jointype == JOIN_SEMI &&
820 bms_equal(sjinfo->syn_righthand, rel2->relids) &&
821 create_unique_path(root, rel2, rel2->cheapest_total_path,
825 * For a semijoin, we can join the RHS to anything else by
826 * unique-ifying the RHS (if the RHS can be unique-ified).
827 * We will only get here if we have the full RHS but less
828 * than min_lefthand on the LHS.
830 * The reason to consider such a join path is exemplified by
831 * SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c)
832 * If we insist on doing this as a semijoin we will first have
833 * to form the cartesian product of A*B. But if we unique-ify
834 * C then the semijoin becomes a plain innerjoin and we can join
835 * in any order, eg C to A and then to B. When C is much smaller
836 * than A and B this can be a huge win. So we allow C to be
837 * joined to just A or just B here, and then make_join_rel has
838 * to handle the case properly.
840 * Note that actually we'll allow unique-ified C to be joined to
841 * some other relation D here, too. That is legal, if usually not
842 * very sane, and this routine is only concerned with legality not
843 * with whether the join is good strategy.
847 return false; /* invalid join path */
848 match_sjinfo = sjinfo;
852 else if (sjinfo->jointype == JOIN_SEMI &&
853 bms_equal(sjinfo->syn_righthand, rel1->relids) &&
854 create_unique_path(root, rel1, rel1->cheapest_total_path,
857 /* Reversed semijoin case */
859 return false; /* invalid join path */
860 match_sjinfo = sjinfo;
867 * Otherwise, the proposed join overlaps the RHS but isn't
868 * a valid implementation of this SJ. It might still be
869 * a legal join, however. If both inputs overlap the RHS,
870 * assume that it's OK. Since the inputs presumably got past
871 * this function's checks previously, they can't overlap the
872 * LHS and their violations of the RHS boundary must represent
873 * SJs that have been determined to commute with this one.
874 * We have to allow this to work correctly in cases like
875 * (a LEFT JOIN (b JOIN (c LEFT JOIN d)))
876 * when the c/d join has been determined to commute with the join
877 * to a, and hence d is not part of min_righthand for the upper
878 * join. It should be legal to join b to c/d but this will appear
879 * as a violation of the upper join's RHS.
880 * Furthermore, if one input overlaps the RHS and the other does
881 * not, we should still allow the join if it is a valid
882 * implementation of some other SJ. We have to allow this to
883 * support the associative identity
884 * (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab
885 * since joining B directly to C violates the lower SJ's RHS.
886 * We assume that make_outerjoininfo() set things up correctly
887 * so that we'll only match to some SJ if the join is valid.
888 * Set flag here to check at bottom of loop.
891 if (sjinfo->jointype != JOIN_SEMI &&
892 bms_overlap(rel1->relids, sjinfo->min_righthand) &&
893 bms_overlap(rel2->relids, sjinfo->min_righthand))
896 Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand));
899 is_valid_inner = false;
904 * Fail if violated some SJ's RHS and didn't match to another SJ. However,
905 * "matching" to a semijoin we are implementing by unique-ification
906 * doesn't count (think: it's really an inner join).
908 if (!is_valid_inner &&
909 (match_sjinfo == NULL || unique_ified))
910 return false; /* invalid join path */
912 /* Otherwise, it's a valid join */
913 *sjinfo_p = match_sjinfo;
914 *reversed_p = reversed;
919 * has_join_restriction
920 * Detect whether the specified relation has join-order restrictions
921 * due to being inside an outer join or an IN (sub-SELECT).
923 * Essentially, this tests whether have_join_order_restriction() could
924 * succeed with this rel and some other one. It's OK if we sometimes
925 * say "true" incorrectly. (Therefore, we don't bother with the relatively
926 * expensive has_legal_joinclause test.)
929 has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
933 foreach(l, root->join_info_list)
935 SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
937 /* ignore full joins --- other mechanisms preserve their ordering */
938 if (sjinfo->jointype == JOIN_FULL)
941 /* ignore if SJ is already contained in rel */
942 if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
943 bms_is_subset(sjinfo->min_righthand, rel->relids))
946 /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
947 if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
948 bms_overlap(sjinfo->min_righthand, rel->relids))
956 * is_dummy_rel --- has relation been proven empty?
959 is_dummy_rel(RelOptInfo *rel)
961 return IS_DUMMY_REL(rel);
965 * Mark a relation as proven empty.
967 * During GEQO planning, this can get invoked more than once on the same
968 * baserel struct, so it's worth checking to see if the rel is already marked
971 * Also, when called during GEQO join planning, we are in a short-lived
972 * memory context. We must make sure that the dummy path attached to a
973 * baserel survives the GEQO cycle, else the baserel is trashed for future
974 * GEQO cycles. On the other hand, when we are marking a joinrel during GEQO,
975 * we don't want the dummy path to clutter the main planning context. Upshot
976 * is that the best solution is to explicitly make the dummy path in the same
977 * context the given RelOptInfo is in.
980 mark_dummy_rel(RelOptInfo *rel)
982 MemoryContext oldcontext;
984 /* Already marked? */
985 if (is_dummy_rel(rel))
988 /* No, so choose correct context to make the dummy path in */
989 oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));
991 /* Set dummy size estimate */
994 /* Evict any previously chosen paths */
997 /* Set up the dummy path */
998 add_path(rel, (Path *) create_append_path(rel, NIL, NULL));
1000 /* Set or update cheapest_total_path and related fields */
1003 MemoryContextSwitchTo(oldcontext);
1007 * restriction_is_constant_false --- is a restrictlist just FALSE?
1009 * In cases where a qual is provably constant FALSE, eval_const_expressions
1010 * will generally have thrown away anything that's ANDed with it. In outer
1011 * join situations this will leave us computing cartesian products only to
1012 * decide there's no match for an outer row, which is pretty stupid. So,
1013 * we need to detect the case.
1015 * If only_pushed_down is TRUE, then consider only pushed-down quals.
1018 restriction_is_constant_false(List *restrictlist, bool only_pushed_down)
1023 * Despite the above comment, the restriction list we see here might
1024 * possibly have other members besides the FALSE constant, since other
1025 * quals could get "pushed down" to the outer join level. So we check
1026 * each member of the list.
1028 foreach(lc, restrictlist)
1030 RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
1032 Assert(IsA(rinfo, RestrictInfo));
1033 if (only_pushed_down && !rinfo->is_pushed_down)
1036 if (rinfo->clause && IsA(rinfo->clause, Const))
1038 Const *con = (Const *) rinfo->clause;
1040 /* constant NULL is as good as constant FALSE for our purposes */
1041 if (con->constisnull)
1043 if (!DatumGetBool(con->constvalue))