diff options
Diffstat (limited to 'src/backend/optimizer/path/joinrels.c')
| -rw-r--r-- | src/backend/optimizer/path/joinrels.c | 29 |
1 files changed, 24 insertions, 5 deletions
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c index c16b2fdf514..3c99c8ce49d 100644 --- a/src/backend/optimizer/path/joinrels.c +++ b/src/backend/optimizer/path/joinrels.c @@ -470,11 +470,30 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2, { /* * 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 we're allowed to associate it into the RHS of this - * SJ. That means this SJ must be a LEFT join (not SEMI or ANTI, - * and certainly not FULL) and the proposed join must not overlap - * the LHS. + * implementation of this SJ. But don't panic quite yet: the RHS + * violation might have occurred previously, in one or both input + * relations, in which case we must have previously decided that + * it was OK to commute some other SJ with this one. If we need + * to perform this join to finish building up the RHS, rejecting + * it could lead to not finding any plan at all. (This can occur + * because of the heuristics elsewhere in this file that postpone + * clauseless joins: we might not consider doing a clauseless join + * within the RHS until after we've performed other, validly + * commutable SJs with one or both sides of the clauseless join.) + * This consideration boils down to the rule that if both inputs + * overlap the RHS, we can allow the join --- they are either + * fully within the RHS, or represent previously-allowed joins to + * rels outside it. + */ + if (bms_overlap(rel1->relids, sjinfo->min_righthand) && + bms_overlap(rel2->relids, sjinfo->min_righthand)) + continue; /* assume valid previous violation of RHS */ + + /* + * The proposed join could still be legal, but only if we're + * allowed to associate it into the RHS of this SJ. That means + * this SJ must be a LEFT join (not SEMI or ANTI, and certainly + * not FULL) and the proposed join must not overlap the LHS. */ if (sjinfo->jointype != JOIN_LEFT || bms_overlap(joinrelids, sjinfo->min_lefthand)) |