diff options
Diffstat (limited to 'src/backend/optimizer/util/joininfo.c')
| -rw-r--r-- | src/backend/optimizer/util/joininfo.c | 24 |
1 files changed, 17 insertions, 7 deletions
diff --git a/src/backend/optimizer/util/joininfo.c b/src/backend/optimizer/util/joininfo.c index b582ccdc004..20d57c51403 100644 --- a/src/backend/optimizer/util/joininfo.c +++ b/src/backend/optimizer/util/joininfo.c @@ -21,34 +21,46 @@ /* * have_relevant_joinclause - * Detect whether there is a joinclause that can be used to join + * Detect whether there is a joinclause that involves * the two given relations. + * + * Note: the joinclause does not have to be evaluatable with only these two + * relations. This is intentional. For example consider + * SELECT * FROM a, b, c WHERE a.x = (b.y + c.z) + * If a is much larger than the other tables, it may be worthwhile to + * cross-join b and c and then use an inner indexscan on a.x. Therefore + * we should consider this joinclause as reason to join b to c, even though + * it can't be applied at that join step. */ bool have_relevant_joinclause(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2) { bool result = false; - Relids join_relids; List *joininfo; + Relids other_relids; ListCell *l; - join_relids = bms_union(rel1->relids, rel2->relids); - /* * We could scan either relation's joininfo list; may as well use the * shorter one. */ if (list_length(rel1->joininfo) <= list_length(rel2->joininfo)) + { joininfo = rel1->joininfo; + other_relids = rel2->relids; + } else + { joininfo = rel2->joininfo; + other_relids = rel1->relids; + } foreach(l, joininfo) { RestrictInfo *rinfo = (RestrictInfo *) lfirst(l); - if (bms_is_subset(rinfo->required_relids, join_relids)) + if (bms_overlap(other_relids, rinfo->required_relids)) { result = true; break; @@ -62,8 +74,6 @@ have_relevant_joinclause(PlannerInfo *root, if (!result && rel1->has_eclass_joins && rel2->has_eclass_joins) result = have_relevant_eclass_joinclause(root, rel1, rel2); - bms_free(join_relids); - return result; } |