diff options
Diffstat (limited to 'src/backend/optimizer/path/joinrels.c')
| -rw-r--r-- | src/backend/optimizer/path/joinrels.c | 135 |
1 files changed, 65 insertions, 70 deletions
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c index f4f2d779b0a..ecb63156860 100644 --- a/src/backend/optimizer/path/joinrels.c +++ b/src/backend/optimizer/path/joinrels.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.75 2005/07/28 22:27:00 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.76 2005/10/15 02:49:20 momjian Exp $ * *------------------------------------------------------------------------- */ @@ -49,17 +49,16 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels) /* * 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. + * 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]. + * 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]) { @@ -76,23 +75,22 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels) if (old_rel->joininfo != NIL) { /* - * 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. + * 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. */ new_rels = make_rels_by_clause_joins(root, old_rel, other_rels); /* - * An exception occurs when there is a clauseless join inside - * an IN (sub-SELECT) construct. Here, the members of the - * subselect all have join clauses (against the stuff outside - * the IN), but they *must* be joined to each other before we - * can make use of those join clauses. So do the clauseless - * join bit. + * An exception occurs when there is a clauseless join inside an + * IN (sub-SELECT) construct. Here, the members of the subselect + * all have join clauses (against the stuff outside the IN), but + * they *must* be joined to each other before we can make use of + * those join clauses. So do the clauseless join bit. * * See also the last-ditch case below. */ @@ -115,30 +113,29 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels) /* * 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. + * 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. + * 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, in order to avoid unreasonable growth of - * planning time. + * suitable join clause, 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. + * 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; @@ -165,8 +162,8 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels) { /* * 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. + * pair of rels. Do so if there is at least one usable + * join clause. */ if (have_relevant_joinclause(old_rel, new_rel)) { @@ -185,16 +182,16 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels) } /* - * 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 + * 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). + * 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) { @@ -318,8 +315,8 @@ make_rels_by_clauseless_joins(PlannerInfo *root, jrel = make_join_rel(root, old_rel, other_rel, JOIN_INNER); /* - * As long as given other_rels are distinct, don't need to - * test to see if jrel is already part of output list. + * 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); @@ -393,10 +390,10 @@ make_jointree_rel(PlannerInfo *root, Node *jtnode) elog(ERROR, "invalid join order"); /* - * Since we are only going to consider this one way to do it, - * we're done generating Paths for this joinrel and can now select - * the cheapest. In fact we *must* do so now, since next level up - * will need it! + * Since we are only going to consider this one way to do it, we're + * done generating Paths for this joinrel and can now select the + * cheapest. In fact we *must* do so now, since next level up will + * need it! */ set_cheapest(rel); @@ -439,10 +436,10 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, joinrelids = bms_union(rel1->relids, rel2->relids); /* - * If we are implementing IN clauses as joins, there are some joins - * that are illegal. Check to see if the proposed join is trouble. We - * can skip the work if looking at an outer join, however, because - * only top-level joins might be affected. + * If we are implementing IN clauses as joins, there are some joins that + * are illegal. Check to see if the proposed join is trouble. We can skip + * the work if looking at an outer join, however, because only top-level + * joins might be affected. */ if (jointype == JOIN_INNER) { @@ -454,8 +451,8 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, /* * This IN clause is not relevant unless its RHS overlaps the - * proposed join. (Check this first as a fast path for - * dismissing most irrelevant INs quickly.) + * proposed join. (Check this first as a fast path for dismissing + * most irrelevant INs quickly.) */ if (!bms_overlap(ininfo->righthand, joinrelids)) continue; @@ -468,10 +465,10 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, continue; /* - * Cannot join if proposed join contains rels not in the RHS - * *and* contains only part of the RHS. We must build the - * complete RHS (subselect's join) before it can be joined to - * rels outside the subselect. + * Cannot join if proposed join contains rels not in the RHS *and* + * contains only part of the RHS. We must build the complete RHS + * (subselect's join) before it can be joined to rels outside the + * subselect. */ if (!bms_is_subset(ininfo->righthand, joinrelids)) { @@ -480,13 +477,12 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, } /* - * At this point we are considering a join of the IN's RHS to - * some other rel(s). + * At this point we are considering a join of the IN's RHS to some + * other rel(s). * - * If we already joined IN's RHS to any other rels in either - * input path, then this join is not constrained (the - * necessary work was done at the lower level where that join - * occurred). + * If we already joined IN's RHS to any other rels in either input + * path, then this join is not constrained (the necessary work was + * done at the lower level where that join occurred). */ if (bms_is_subset(ininfo->righthand, rel1->relids) && !bms_equal(ininfo->righthand, rel1->relids)) @@ -500,12 +496,11 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, * innerrel is exactly RHS; conversely JOIN_REVERSE_IN handles * RHS/LHS. * - * JOIN_UNIQUE_OUTER will work if outerrel is exactly RHS; - * conversely JOIN_UNIQUE_INNER will work if innerrel is - * exactly RHS. + * JOIN_UNIQUE_OUTER will work if outerrel is exactly RHS; conversely + * JOIN_UNIQUE_INNER will work if innerrel is exactly RHS. * - * But none of these will work if we already found another IN - * that needs to trigger here. + * But none of these will work if we already found another IN that + * needs to trigger here. */ if (jointype != JOIN_INNER) { @@ -532,8 +527,8 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, } /* - * Find or build the join RelOptInfo, and compute the restrictlist - * that goes with this particular joining. + * Find or build the join RelOptInfo, and compute the restrictlist that + * goes with this particular joining. */ joinrel = build_join_rel(root, joinrelids, rel1, rel2, jointype, &restrictlist); |