diff options
Diffstat (limited to 'contrib/postgres_fdw/postgres_fdw.c')
| -rw-r--r-- | contrib/postgres_fdw/postgres_fdw.c | 34 |
1 files changed, 23 insertions, 11 deletions
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index 4e31b8e40dd..4b6ec14c65b 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -3952,14 +3952,6 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid) * Assess whether the join between inner and outer relations can be pushed down * to the foreign server. As a side effect, save information we obtain in this * function to PgFdwRelationInfo passed in. - * - * Joins that satisfy conditions below are safe to push down. - * - * 1) Join type is INNER or OUTER (one of LEFT/RIGHT/FULL) - * 2) Both outer and inner portions are safe to push-down - * 3) All join conditions are safe to push down - * 4) No relation has local filter (this can be relaxed for INNER JOIN, if we - * can move unpushable clauses upwards in the join tree). */ static bool foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, @@ -4036,6 +4028,26 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, return false; } + /* + * deparseExplicitTargetList() isn't smart enough to handle anything other + * than a Var. In particular, if there's some PlaceHolderVar that would + * need to be evaluated within this join tree (because there's an upper + * reference to a quantity that may go to NULL as a result of an outer + * join), then we can't try to push the join down because we'll fail when + * we get to deparseExplicitTargetList(). However, a PlaceHolderVar that + * needs to be evaluated *at the top* of this join tree is OK, because we + * can do that locally after fetching the results from the remote side. + */ + foreach(lc, root->placeholder_list) + { + PlaceHolderInfo *phinfo = lfirst(lc); + Relids relids = joinrel->relids; + + if (bms_is_subset(phinfo->ph_eval_at, relids) && + bms_nonempty_difference(relids, phinfo->ph_eval_at)) + return false; + } + /* Save the join clauses, for later use. */ fpinfo->joinclauses = joinclauses; @@ -4116,9 +4128,9 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, } /* - * For an inner join, as explained above all restrictions can be treated - * alike. Treating the pushed down conditions as join conditions allows a - * top level full outer join to be deparsed without requiring subqueries. + * For an inner join, all restrictions can be treated alike. Treating the + * pushed down conditions as join conditions allows a top level full outer + * join to be deparsed without requiring subqueries. */ if (jointype == JOIN_INNER) { |