/*------------------------------------------------------------------------- * * joinrels.c * Routines to determine which relations should be joined * * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.98 2009/02/19 20:32:45 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include "optimizer/joininfo.h" #include "optimizer/pathnode.h" #include "optimizer/paths.h" static List *make_rels_by_clause_joins(PlannerInfo *root, RelOptInfo *old_rel, ListCell *other_rels); static List *make_rels_by_clauseless_joins(PlannerInfo *root, RelOptInfo *old_rel, ListCell *other_rels); static bool has_join_restriction(PlannerInfo *root, RelOptInfo *rel); static bool has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel); static bool is_dummy_rel(RelOptInfo *rel); static void mark_dummy_rel(RelOptInfo *rel); static bool restriction_is_constant_false(List *restrictlist); /* * join_search_one_level * Consider ways to produce join relations containing exactly 'level' * jointree items. (This is one step of the dynamic-programming method * embodied in standard_join_search.) Join rel nodes for each feasible * combination of lower-level rels are created and returned in a list. * Implementation paths are created for each such joinrel, too. * * level: level of rels we want to make this time. * joinrels[j], 1 <= j < level, is a list of rels containing j items. */ List * join_search_one_level(PlannerInfo *root, int level, List **joinrels) { List *result_rels = NIL; List *new_rels; ListCell *r; int k; /* * First, consider left-sided and right-sided plans, in which rels of * exactly level-1 member relations are joined against initial relations. * We prefer to join using join clauses, but if we find a rel of level-1 * members that has no join clauses, we will generate Cartesian-product * joins against all initial rels not already contained in it. * * In the first pass (level == 2), we try to join each initial rel to each * initial rel that appears later in joinrels[1]. (The mirror-image joins * are handled automatically by make_join_rel.) In later passes, we try * to join rels of size level-1 from joinrels[level-1] to each initial rel * in joinrels[1]. */ foreach(r, joinrels[level - 1]) { RelOptInfo *old_rel = (RelOptInfo *) lfirst(r); ListCell *other_rels; if (level == 2) other_rels = lnext(r); /* only consider remaining initial * rels */ else other_rels = list_head(joinrels[1]); /* consider all initial * rels */ if (old_rel->joininfo != NIL || old_rel->has_eclass_joins || has_join_restriction(root, old_rel)) { /* * Note that if all available join clauses for this rel require * more than one other rel, we will fail to make any joins against * it here. In most cases that's OK; it'll be considered by * "bushy plan" join code in a higher-level pass where we have * those other rels collected into a join rel. * * See also the last-ditch case below. */ new_rels = make_rels_by_clause_joins(root, old_rel, other_rels); } else { /* * Oops, we have a relation that is not joined to any other * relation, either directly or by join-order restrictions. * Cartesian product time. */ new_rels = make_rels_by_clauseless_joins(root, old_rel, other_rels); } /* * At levels above 2 we will generate the same joined relation in * multiple ways --- for example (a join b) join c is the same * RelOptInfo as (b join c) join a, though the second case will add a * different set of Paths to it. To avoid making extra work for * subsequent passes, do not enter the same RelOptInfo into our output * list multiple times. */ result_rels = list_concat_unique_ptr(result_rels, new_rels); } /* * Now, consider "bushy plans" in which relations of k initial rels are * joined to relations of level-k initial rels, for 2 <= k <= level-2. * * We only consider bushy-plan joins for pairs of rels where there is a * suitable join clause (or join order restriction), in order to avoid * unreasonable growth of planning time. */ for (k = 2;; k++) { int other_level = level - k; /* * Since make_join_rel(x, y) handles both x,y and y,x cases, we only * need to go as far as the halfway point. */ if (k > other_level) break; foreach(r, joinrels[k]) { RelOptInfo *old_rel = (RelOptInfo *) lfirst(r); ListCell *other_rels; ListCell *r2; /* * We can ignore clauseless joins here, *except* when they * participate in join-order restrictions --- then we might have * to force a bushy join plan. */ if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins && !has_join_restriction(root, old_rel)) continue; if (k == other_level) other_rels = lnext(r); /* only consider remaining rels */ else other_rels = list_head(joinrels[other_level]); for_each_cell(r2, other_rels) { RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2); if (!bms_overlap(old_rel->relids, new_rel->relids)) { /* * OK, we can build a rel of the right level from this * pair of rels. Do so if there is at least one usable * join clause or a relevant join restriction. */ if (have_relevant_joinclause(root, old_rel, new_rel) || have_join_order_restriction(root, old_rel, new_rel)) { RelOptInfo *jrel; jrel = make_join_rel(root, old_rel, new_rel); /* Avoid making duplicate entries ... */ if (jrel) result_rels = list_append_unique_ptr(result_rels, jrel); } } } } } /* * Last-ditch effort: if we failed to find any usable joins so far, force * a set of cartesian-product joins to be generated. This handles the * special case where all the available rels have join clauses but we * cannot use any of the joins yet. An example is * * SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0; * * The join clause will be usable at level 3, but at level 2 we have no * choice but to make cartesian joins. We consider only left-sided and * right-sided cartesian joins in this case (no bushy). */ if (result_rels == NIL) { /* * This loop is just like the first one, except we always call * make_rels_by_clauseless_joins(). */ foreach(r, joinrels[level - 1]) { RelOptInfo *old_rel = (RelOptInfo *) lfirst(r); ListCell *other_rels; if (level == 2) other_rels = lnext(r); /* only consider remaining initial * rels */ else other_rels = list_head(joinrels[1]); /* consider all initial * rels */ new_rels = make_rels_by_clauseless_joins(root, old_rel, other_rels); result_rels = list_concat_unique_ptr(result_rels, new_rels); } /*---------- * When special joins are involved, there may be no legal way * to make an N-way join for some values of N. For example consider * * SELECT ... FROM t1 WHERE * x IN (SELECT ... FROM t2,t3 WHERE ...) AND * y IN (SELECT ... FROM t4,t5 WHERE ...) * * We will flatten this query to a 5-way join problem, but there are * no 4-way joins that join_is_legal() will consider legal. We have * to accept failure at level 4 and go on to discover a workable * bushy plan at level 5. * * However, if there are no special joins then join_is_legal() should * never fail, and so the following sanity check is useful. *---------- */ if (result_rels == NIL && root->join_info_list == NIL) elog(ERROR, "failed to build any %d-way joins", level); } return result_rels; } /* * make_rels_by_clause_joins * Build joins between the given relation 'old_rel' and other relations * that participate in join clauses that 'old_rel' also participates in * (or participate in join-order restrictions with it). * The join rel nodes are returned in a list. * * 'old_rel' is the relation entry for the relation to be joined * 'other_rels': the first cell in a linked list containing the other * rels to be considered for joining * * Currently, this is only used with initial rels in other_rels, but it * will work for joining to joinrels too. */ static List * make_rels_by_clause_joins(PlannerInfo *root, RelOptInfo *old_rel, ListCell *other_rels) { List *result = NIL; ListCell *l; for_each_cell(l, other_rels) { RelOptInfo *other_rel = (RelOptInfo *) lfirst(l); if (!bms_overlap(old_rel->relids, other_rel->relids) && (have_relevant_joinclause(root, old_rel, other_rel) || have_join_order_restriction(root, old_rel, other_rel))) { RelOptInfo *jrel; jrel = make_join_rel(root, old_rel, other_rel); if (jrel) result = lcons(jrel, result); } } return result; } /* * make_rels_by_clauseless_joins * Given a relation 'old_rel' and a list of other relations * 'other_rels', create a join relation between 'old_rel' and each * member of 'other_rels' that isn't already included in 'old_rel'. * The join rel nodes are returned in a list. * * 'old_rel' is the relation entry for the relation to be joined * 'other_rels': the first cell of a linked list containing the * other rels to be considered for joining * * Currently, this is only used with initial rels in other_rels, but it would * work for joining to joinrels too. */ static List * make_rels_by_clauseless_joins(PlannerInfo *root, RelOptInfo *old_rel, ListCell *other_rels) { List *result = NIL; ListCell *i; for_each_cell(i, other_rels) { RelOptInfo *other_rel = (RelOptInfo *) lfirst(i); if (!bms_overlap(other_rel->relids, old_rel->relids)) { RelOptInfo *jrel; jrel = make_join_rel(root, old_rel, other_rel); /* * As long as given other_rels are distinct, don't need to test to * see if jrel is already part of output list. */ if (jrel) result = lcons(jrel, result); } } return result; } /* * join_is_legal * Determine whether a proposed join is legal given the query's * join order constraints; and if it is, determine the join type. * * Caller must supply not only the two rels, but the union of their relids. * (We could simplify the API by computing joinrelids locally, but this * would be redundant work in the normal path through make_join_rel.) * * On success, *sjinfo_p is set to NULL if this is to be a plain inner join, * else it's set to point to the associated SpecialJoinInfo node. Also, * *reversed_p is set TRUE if the given relations need to be swapped to * match the SpecialJoinInfo node. */ static bool join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, Relids joinrelids, SpecialJoinInfo **sjinfo_p, bool *reversed_p) { SpecialJoinInfo *match_sjinfo; bool reversed; bool is_valid_inner; ListCell *l; /* * Ensure output params are set on failure return. This is just to * suppress uninitialized-variable warnings from overly anal compilers. */ *sjinfo_p = NULL; *reversed_p = false; /* * If we have any special joins, the proposed join might be illegal; and * in any case we have to determine its join type. Scan the join info * list for conflicts. */ match_sjinfo = NULL; reversed = false; is_valid_inner = true; foreach(l, root->join_info_list) { SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l); /* * This special join is not relevant unless its RHS overlaps the * proposed join. (Check this first as a fast path for dismissing * most irrelevant SJs quickly.) */ if (!bms_overlap(sjinfo->min_righthand, joinrelids)) continue; /* * Also, not relevant if proposed join is fully contained within RHS * (ie, we're still building up the RHS). */ if (bms_is_subset(joinrelids, sjinfo->min_righthand)) continue; /* * Also, not relevant if SJ is already done within either input. */ if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) && bms_is_subset(sjinfo->min_righthand, rel1->relids)) continue; if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) && bms_is_subset(sjinfo->min_righthand, rel2->relids)) continue; /* * If one input contains min_lefthand and the other contains * min_righthand, then we can perform the SJ at this join. * * Barf if we get matches to more than one SJ (is that possible?) */ if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) && bms_is_subset(sjinfo->min_righthand, rel2->relids)) { if (match_sjinfo) return false; /* invalid join path */ match_sjinfo = sjinfo; reversed = false; } else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) && bms_is_subset(sjinfo->min_righthand, rel1->relids)) { if (match_sjinfo) return false; /* invalid join path */ match_sjinfo = sjinfo; reversed = true; } else if (sjinfo->jointype == JOIN_SEMI && bms_equal(sjinfo->syn_righthand, rel2->relids) && create_unique_path(root, rel2, rel2->cheapest_total_path, sjinfo) != NULL) { /*---------- * For a semijoin, we can join the RHS to anything else by * unique-ifying the RHS (if the RHS can be unique-ified). * We will only get here if we have the full RHS but less * than min_lefthand on the LHS. * * The reason to consider such a join path is exemplified by * SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c) * If we insist on doing this as a semijoin we will first have * to form the cartesian product of A*B. But if we unique-ify * C then the semijoin becomes a plain innerjoin and we can join * in any order, eg C to A and then to B. When C is much smaller * than A and B this can be a huge win. So we allow C to be * joined to just A or just B here, and then make_join_rel has * to handle the case properly. * * Note that actually we'll allow unique-ified C to be joined to * some other relation D here, too. That is legal, if usually not * very sane, and this routine is only concerned with legality not * with whether the join is good strategy. *---------- */ if (match_sjinfo) return false; /* invalid join path */ match_sjinfo = sjinfo; reversed = false; } else if (sjinfo->jointype == JOIN_SEMI && bms_equal(sjinfo->syn_righthand, rel1->relids) && create_unique_path(root, rel1, rel1->cheapest_total_path, sjinfo) != NULL) { /* Reversed semijoin case */ if (match_sjinfo) return false; /* invalid join path */ match_sjinfo = sjinfo; reversed = true; } else { /*---------- * Otherwise, the proposed join overlaps the RHS but isn't * a valid implementation of this SJ. It might still be * a legal join, however. If both inputs overlap the RHS, * assume that it's OK. Since the inputs presumably got past * this function's checks previously, they can't overlap the * LHS and their violations of the RHS boundary must represent * SJs that have been determined to commute with this one. * We have to allow this to work correctly in cases like * (a LEFT JOIN (b JOIN (c LEFT JOIN d))) * when the c/d join has been determined to commute with the join * to a, and hence d is not part of min_righthand for the upper * join. It should be legal to join b to c/d but this will appear * as a violation of the upper join's RHS. * Furthermore, if one input overlaps the RHS and the other does * not, we should still allow the join if it is a valid * implementation of some other SJ. We have to allow this to * support the associative identity * (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab * since joining B directly to C violates the lower SJ's RHS. * We assume that make_outerjoininfo() set things up correctly * so that we'll only match to some SJ if the join is valid. * Set flag here to check at bottom of loop. * * For a semijoin, assume it's okay if either side fully contains * the RHS (per the unique-ification case above). *---------- */ if (sjinfo->jointype != JOIN_SEMI && bms_overlap(rel1->relids, sjinfo->min_righthand) && bms_overlap(rel2->relids, sjinfo->min_righthand)) { /* seems OK */ Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand)); } else if (sjinfo->jointype == JOIN_SEMI && (bms_is_subset(sjinfo->syn_righthand, rel1->relids) || bms_is_subset(sjinfo->syn_righthand, rel2->relids))) { /* seems OK */ } else is_valid_inner = false; } } /* Fail if violated some SJ's RHS and didn't match to another SJ */ if (match_sjinfo == NULL && !is_valid_inner) return false; /* invalid join path */ /* Otherwise, it's a valid join */ *sjinfo_p = match_sjinfo; *reversed_p = reversed; return true; } /* * make_join_rel * Find or create a join RelOptInfo that represents the join of * the two given rels, and add to it path information for paths * created with the two rels as outer and inner rel. * (The join rel may already contain paths generated from other * pairs of rels that add up to the same set of base rels.) * * NB: will return NULL if attempted join is not valid. This can happen * when working with outer joins, or with IN or EXISTS clauses that have been * turned into joins. */ RelOptInfo * make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2) { Relids joinrelids; SpecialJoinInfo *sjinfo; bool reversed; SpecialJoinInfo sjinfo_data; RelOptInfo *joinrel; List *restrictlist; /* We should never try to join two overlapping sets of rels. */ Assert(!bms_overlap(rel1->relids, rel2->relids)); /* Construct Relids set that identifies the joinrel. */ joinrelids = bms_union(rel1->relids, rel2->relids); /* Check validity and determine join type. */ if (!join_is_legal(root, rel1, rel2, joinrelids, &sjinfo, &reversed)) { /* invalid join path */ bms_free(joinrelids); return NULL; } /* Swap rels if needed to match the join info. */ if (reversed) { RelOptInfo *trel = rel1; rel1 = rel2; rel2 = trel; } /* * If it's a plain inner join, then we won't have found anything in * join_info_list. Make up a SpecialJoinInfo so that selectivity * estimation functions will know what's being joined. */ if (sjinfo == NULL) { sjinfo = &sjinfo_data; sjinfo->type = T_SpecialJoinInfo; sjinfo->min_lefthand = rel1->relids; sjinfo->min_righthand = rel2->relids; sjinfo->syn_lefthand = rel1->relids; sjinfo->syn_righthand = rel2->relids; sjinfo->jointype = JOIN_INNER; /* we don't bother trying to make the remaining fields valid */ sjinfo->lhs_strict = false; sjinfo->delay_upper_joins = false; sjinfo->join_quals = NIL; } /* * Find or build the join RelOptInfo, and compute the restrictlist that * goes with this particular joining. */ joinrel = build_join_rel(root, joinrelids, rel1, rel2, sjinfo, &restrictlist); /* * If we've already proven this join is empty, we needn't consider * any more paths for it. */ if (is_dummy_rel(joinrel)) { bms_free(joinrelids); return joinrel; } /* * Consider paths using each rel as both outer and inner. Depending * on the join type, a provably empty outer or inner rel might mean * the join is provably empty too; in which case throw away any * previously computed paths and mark the join as dummy. (We do it * this way since it's conceivable that dummy-ness of a multi-element * join might only be noticeable for certain construction paths.) * * Also, a provably constant-false join restriction typically means that * we can skip evaluating one or both sides of the join. We do this * by marking the appropriate rel as dummy. * * We need only consider the jointypes that appear in join_info_list, * plus JOIN_INNER. */ switch (sjinfo->jointype) { case JOIN_INNER: if (is_dummy_rel(rel1) || is_dummy_rel(rel2) || restriction_is_constant_false(restrictlist)) { mark_dummy_rel(joinrel); break; } add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_INNER, sjinfo, restrictlist); add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_INNER, sjinfo, restrictlist); break; case JOIN_LEFT: if (is_dummy_rel(rel1)) { mark_dummy_rel(joinrel); break; } if (restriction_is_constant_false(restrictlist) && bms_is_subset(rel2->relids, sjinfo->syn_righthand)) mark_dummy_rel(rel2); add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_LEFT, sjinfo, restrictlist); add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_RIGHT, sjinfo, restrictlist); break; case JOIN_FULL: if (is_dummy_rel(rel1) && is_dummy_rel(rel2)) { mark_dummy_rel(joinrel); break; } add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_FULL, sjinfo, restrictlist); add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_FULL, sjinfo, restrictlist); break; case JOIN_SEMI: /* * We might have a normal semijoin, or a case where we don't have * enough rels to do the semijoin but can unique-ify the RHS and * then do an innerjoin (see comments in join_is_legal). In the * latter case we can't apply JOIN_SEMI joining. */ if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) && bms_is_subset(sjinfo->min_righthand, rel2->relids)) { if (is_dummy_rel(rel1) || is_dummy_rel(rel2) || restriction_is_constant_false(restrictlist)) { mark_dummy_rel(joinrel); break; } add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_SEMI, sjinfo, restrictlist); } /* * If we know how to unique-ify the RHS and one input rel is * exactly the RHS (not a superset) we can consider unique-ifying * it and then doing a regular join. (The create_unique_path * check here is probably redundant with what join_is_legal did, * but if so the check is cheap because it's cached. So test * anyway to be sure.) */ if (bms_equal(sjinfo->syn_righthand, rel2->relids) && create_unique_path(root, rel2, rel2->cheapest_total_path, sjinfo) != NULL) { add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_INNER, sjinfo, restrictlist); add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_OUTER, sjinfo, restrictlist); } break; case JOIN_ANTI: if (is_dummy_rel(rel1)) { mark_dummy_rel(joinrel); break; } if (restriction_is_constant_false(restrictlist) && bms_is_subset(rel2->relids, sjinfo->syn_righthand)) mark_dummy_rel(rel2); add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_ANTI, sjinfo, restrictlist); break; default: /* other values not expected here */ elog(ERROR, "unrecognized join type: %d", (int) sjinfo->jointype); break; } bms_free(joinrelids); return joinrel; } /* * have_join_order_restriction * Detect whether the two relations should be joined to satisfy * a join-order restriction arising from special joins. * * In practice this is always used with have_relevant_joinclause(), and so * could be merged with that function, but it seems clearer to separate the * two concerns. We need these tests because there are degenerate cases where * a clauseless join must be performed to satisfy join-order restrictions. * * Note: this is only a problem if one side of a degenerate outer join * contains multiple rels, or a clauseless join is required within an * IN/EXISTS RHS; else we will find a join path via the "last ditch" case in * join_search_one_level(). We could dispense with this test if we were * willing to try bushy plans in the "last ditch" case, but that seems much * less efficient. */ bool have_join_order_restriction(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2) { bool result = false; ListCell *l; /* * It's possible that the rels correspond to the left and right sides of a * degenerate outer join, that is, one with no joinclause mentioning the * non-nullable side; in which case we should force the join to occur. * * Also, the two rels could represent a clauseless join that has to be * completed to build up the LHS or RHS of an outer join. */ foreach(l, root->join_info_list) { SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l); /* ignore full joins --- other mechanisms handle them */ if (sjinfo->jointype == JOIN_FULL) continue; /* Can we perform the SJ with these rels? */ if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) && bms_is_subset(sjinfo->min_righthand, rel2->relids)) { result = true; break; } if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) && bms_is_subset(sjinfo->min_righthand, rel1->relids)) { result = true; break; } /* * Might we need to join these rels to complete the RHS? We have to * use "overlap" tests since either rel might include a lower SJ that * has been proven to commute with this one. */ if (bms_overlap(sjinfo->min_righthand, rel1->relids) && bms_overlap(sjinfo->min_righthand, rel2->relids)) { result = true; break; } /* Likewise for the LHS. */ if (bms_overlap(sjinfo->min_lefthand, rel1->relids) && bms_overlap(sjinfo->min_lefthand, rel2->relids)) { result = true; break; } } /* * We do not force the join to occur if either input rel can legally be * joined to anything else using joinclauses. This essentially means that * clauseless bushy joins are put off as long as possible. The reason is * that when there is a join order restriction high up in the join tree * (that is, with many rels inside the LHS or RHS), we would otherwise * expend lots of effort considering very stupid join combinations within * its LHS or RHS. */ if (result) { if (has_legal_joinclause(root, rel1) || has_legal_joinclause(root, rel2)) result = false; } return result; } /* * has_join_restriction * Detect whether the specified relation has join-order restrictions * due to being inside an outer join or an IN (sub-SELECT). * * Essentially, this tests whether have_join_order_restriction() could * succeed with this rel and some other one. It's OK if we sometimes * say "true" incorrectly. (Therefore, we don't bother with the relatively * expensive has_legal_joinclause test.) */ static bool has_join_restriction(PlannerInfo *root, RelOptInfo *rel) { ListCell *l; foreach(l, root->join_info_list) { SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l); /* ignore full joins --- other mechanisms preserve their ordering */ if (sjinfo->jointype == JOIN_FULL) continue; /* ignore if SJ is already contained in rel */ if (bms_is_subset(sjinfo->min_lefthand, rel->relids) && bms_is_subset(sjinfo->min_righthand, rel->relids)) continue; /* restricted if it overlaps LHS or RHS, but doesn't contain SJ */ if (bms_overlap(sjinfo->min_lefthand, rel->relids) || bms_overlap(sjinfo->min_righthand, rel->relids)) return true; } return false; } /* * has_legal_joinclause * Detect whether the specified relation can legally be joined * to any other rels using join clauses. * * We consider only joins to single other relations in the current * initial_rels list. This is sufficient to get a "true" result in most real * queries, and an occasional erroneous "false" will only cost a bit more * planning time. The reason for this limitation is that considering joins to * other joins would require proving that the other join rel can legally be * formed, which seems like too much trouble for something that's only a * heuristic to save planning time. (Note: we must look at initial_rels * and not all of the query, since when we are planning a sub-joinlist we * may be forced to make clauseless joins within initial_rels even though * there are join clauses linking to other parts of the query.) */ static bool has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel) { ListCell *lc; foreach(lc, root->initial_rels) { RelOptInfo *rel2 = (RelOptInfo *) lfirst(lc); /* ignore rels that are already in "rel" */ if (bms_overlap(rel->relids, rel2->relids)) continue; if (have_relevant_joinclause(root, rel, rel2)) { Relids joinrelids; SpecialJoinInfo *sjinfo; bool reversed; /* join_is_legal needs relids of the union */ joinrelids = bms_union(rel->relids, rel2->relids); if (join_is_legal(root, rel, rel2, joinrelids, &sjinfo, &reversed)) { /* Yes, this will work */ bms_free(joinrelids); return true; } bms_free(joinrelids); } } return false; } /* * is_dummy_rel --- has relation been proven empty? * * If so, it will have a single path that is dummy. */ static bool is_dummy_rel(RelOptInfo *rel) { return (rel->cheapest_total_path != NULL && IS_DUMMY_PATH(rel->cheapest_total_path)); } /* * Mark a rel as proven empty. */ static void mark_dummy_rel(RelOptInfo *rel) { /* Set dummy size estimate */ rel->rows = 0; /* Evict any previously chosen paths */ rel->pathlist = NIL; /* Set up the dummy path */ add_path(rel, (Path *) create_append_path(rel, NIL)); /* Set or update cheapest_total_path */ set_cheapest(rel); } /* * restriction_is_constant_false --- is a restrictlist just FALSE? * * In cases where a qual is provably constant FALSE, eval_const_expressions * will generally have thrown away anything that's ANDed with it. In outer * join situations this will leave us computing cartesian products only to * decide there's no match for an outer row, which is pretty stupid. So, * we need to detect the case. */ static bool restriction_is_constant_false(List *restrictlist) { ListCell *lc; /* * Despite the above comment, the restriction list we see here might * possibly have other members besides the FALSE constant, since other * quals could get "pushed down" to the outer join level. So we check * each member of the list. */ foreach(lc, restrictlist) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc); Assert(IsA(rinfo, RestrictInfo)); if (rinfo->clause && IsA(rinfo->clause, Const)) { Const *con = (Const *) rinfo->clause; /* constant NULL is as good as constant FALSE for our purposes */ if (con->constisnull) return true; if (!DatumGetBool(con->constvalue)) return true; } } return false; }