diff options
Diffstat (limited to 'src/backend/optimizer/path/equivclass.c')
| -rw-r--r-- | src/backend/optimizer/path/equivclass.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c index a20ed5f36c7..e44e960b545 100644 --- a/src/backend/optimizer/path/equivclass.c +++ b/src/backend/optimizer/path/equivclass.c @@ -1611,8 +1611,8 @@ exprs_known_equal(PlannerInfo *root, Node *item1, Node *item2) * Search for EC members that reference (only) the parent_rel, and * add transformed members referencing the child_rel. * - * We only need to do this for ECs that could generate join conditions, - * since the child members are only used for creating inner-indexscan paths. + * Note that this function won't be called at all unless we have at least some + * reason to believe that the EC members it generates will be useful. * * parent_rel and child_rel could be derived from appinfo, but since the * caller has already computed them, we might as well just pass them in. @@ -1631,10 +1631,14 @@ add_child_rel_equivalences(PlannerInfo *root, ListCell *lc2; /* - * Won't generate joinclauses if const or single-member (the latter - * test covers the volatile case too) + * If this EC contains a constant, then it's not useful for sorting + * or driving an inner index-scan, so we skip generating child EMs. + * + * If this EC contains a volatile expression, then generating child + * EMs would be downright dangerous. We rely on a volatile EC having + * only one EM. */ - if (cur_ec->ec_has_const || list_length(cur_ec->ec_members) <= 1) + if (cur_ec->ec_has_const || cur_ec->ec_has_volatile) continue; /* No point in searching if parent rel not mentioned in eclass */ |