From d468da0d65905b762dbaa647aaf8ba1ea5bca04d Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 7 Feb 2019 13:10:46 -0500 Subject: [PATCH] Ensure that foreign scans with lateral refs are planned correctly. As reported in bug #15613 from Srinivasan S A, file_fdw and postgres_fdw neglected to mark plain baserel foreign paths as parameterized when the relation has lateral_relids. Other FDWs have surely copied this mistake, so rather than just patching those two modules, install a band-aid fix in create_foreignscan_path to rectify the mistake centrally. Although the band-aid is enough to fix the visible symptom, correct the calls in file_fdw and postgres_fdw anyway, so that they are valid examples for external FDWs. Also, since the band-aid isn't enough to make this work for parameterized foreign joins, throw an elog(ERROR) if such a case is passed to create_foreignscan_path. This shouldn't pose much of a problem for existing external FDWs, since it's likely they aren't trying to make such paths anyway (though some of them may need a defense against joins with lateral_relids, similar to the one this patch installs into postgres_fdw). Add some assertions in relnode.c to catch future occurrences of the same error --- in particular, as backstop against core-code mistakes like the one fixed by commit bdd9a99aa. Discussion: https://postgr.es/m/15613-092be1be9576c728@postgresql.org --- contrib/file_fdw/file_fdw.c | 6 +- .../postgres_fdw/expected/postgres_fdw.out | 56 +++++++++++++++++++ contrib/postgres_fdw/postgres_fdw.c | 16 +++++- contrib/postgres_fdw/sql/postgres_fdw.sql | 26 +++++++++ src/backend/optimizer/util/pathnode.c | 23 ++++++++ src/backend/optimizer/util/relnode.c | 9 +++ 6 files changed, 132 insertions(+), 4 deletions(-) diff --git a/contrib/file_fdw/file_fdw.c b/contrib/file_fdw/file_fdw.c index b42de873e0..fc53d4fa5e 100644 --- a/contrib/file_fdw/file_fdw.c +++ b/contrib/file_fdw/file_fdw.c @@ -521,6 +521,10 @@ fileGetForeignPaths(PlannerInfo *root, * Create a ForeignPath node and add it as only possible path. We use the * fdw_private list of the path to carry the convert_selectively option; * it will be propagated into the fdw_private list of the Plan node. + * + * We don't support pushing join clauses into the quals of this path, but + * it could still have required parameterization due to LATERAL refs in + * its tlist. */ add_path(baserel, (Path *) create_foreignscan_path(root, baserel, @@ -529,7 +533,7 @@ fileGetForeignPaths(PlannerInfo *root, startup_cost, total_cost, NIL, /* no pathkeys */ - NULL, /* no outer rel either */ + baserel->lateral_relids, NULL, /* no extra plan */ coptions)); diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index de4a1b6df8..020350fb37 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -2132,6 +2132,62 @@ SELECT t1."C 1" FROM "S 1"."T 1" t1, LATERAL (SELECT DISTINCT t2.c1, t3.c1 FROM 1 (10 rows) +-- bug #15613: bad plan for foreign table scan with lateral reference +EXPLAIN (VERBOSE, COSTS OFF) +SELECT ref_0.c2, subq_1.* +FROM + "S 1"."T 1" AS ref_0, + LATERAL ( + SELECT ref_0."C 1" c1, subq_0.* + FROM (SELECT ref_0.c2, ref_1.c3 + FROM ft1 AS ref_1) AS subq_0 + RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3) + ) AS subq_1 +WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001' +ORDER BY ref_0."C 1"; + QUERY PLAN +--------------------------------------------------------------------------------------------------------- + Nested Loop + Output: ref_0.c2, ref_0."C 1", (ref_0.c2), ref_1.c3, ref_0."C 1" + -> Nested Loop + Output: ref_0.c2, ref_0."C 1", ref_1.c3, (ref_0.c2) + -> Index Scan using t1_pkey on "S 1"."T 1" ref_0 + Output: ref_0."C 1", ref_0.c2, ref_0.c3, ref_0.c4, ref_0.c5, ref_0.c6, ref_0.c7, ref_0.c8 + Index Cond: (ref_0."C 1" < 10) + -> Foreign Scan on public.ft1 ref_1 + Output: ref_1.c3, ref_0.c2 + Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE ((c3 = '00001'::text)) + -> Materialize + Output: ref_3.c3 + -> Foreign Scan on public.ft2 ref_3 + Output: ref_3.c3 + Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE ((c3 = '00001'::text)) +(15 rows) + +SELECT ref_0.c2, subq_1.* +FROM + "S 1"."T 1" AS ref_0, + LATERAL ( + SELECT ref_0."C 1" c1, subq_0.* + FROM (SELECT ref_0.c2, ref_1.c3 + FROM ft1 AS ref_1) AS subq_0 + RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3) + ) AS subq_1 +WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001' +ORDER BY ref_0."C 1"; + c2 | c1 | c2 | c3 +----+----+----+------- + 1 | 1 | 1 | 00001 + 2 | 2 | 2 | 00001 + 3 | 3 | 3 | 00001 + 4 | 4 | 4 | 00001 + 5 | 5 | 5 | 00001 + 6 | 6 | 6 | 00001 + 7 | 7 | 7 | 00001 + 8 | 8 | 8 | 00001 + 9 | 9 | 9 | 00001 +(9 rows) + -- non-Var items in targetlist of the nullable rel of a join preventing -- push-down in some cases -- unable to push {ft1, ft2} diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index 309f27ca85..1326fcf822 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -893,6 +893,9 @@ postgresGetForeignPaths(PlannerInfo *root, * baserestrict conditions we were able to send to remote, there might * actually be an indexscan happening there). We already did all the work * to estimate cost and size of this path. + * + * Although this path uses no join clauses, it could still have required + * parameterization due to LATERAL refs in its tlist. */ path = create_foreignscan_path(root, baserel, NULL, /* default pathtarget */ @@ -900,7 +903,7 @@ postgresGetForeignPaths(PlannerInfo *root, fpinfo->startup_cost, fpinfo->total_cost, NIL, /* no pathkeys */ - NULL, /* no outer rel either */ + baserel->lateral_relids, NULL, /* no extra plan */ NIL); /* no fdw_private list */ add_path(baserel, (Path *) path); @@ -4243,7 +4246,7 @@ add_paths_with_pathkeys_for_rel(PlannerInfo *root, RelOptInfo *rel, startup_cost, total_cost, useful_pathkeys, - NULL, + rel->lateral_relids, sorted_epq_path, NIL)); } @@ -4276,6 +4279,13 @@ postgresGetForeignJoinPaths(PlannerInfo *root, if (joinrel->fdw_private) return; + /* + * This code does not work for joins with lateral references, since those + * must have parameterized paths, which we don't generate yet. + */ + if (!bms_is_empty(joinrel->lateral_relids)) + return; + /* * Create unfinished PgFdwRelationInfo entry which is used to indicate * that the join relation is already considered, so that we won't waste @@ -4367,7 +4377,7 @@ postgresGetForeignJoinPaths(PlannerInfo *root, startup_cost, total_cost, NIL, /* no pathkeys */ - NULL, /* no required_outer */ + joinrel->lateral_relids, epq_path, NULL); /* no fdw_private */ diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 3e488e0ebe..e424ebbe1d 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -516,6 +516,32 @@ EXPLAIN (VERBOSE, COSTS OFF) SELECT t1."C 1" FROM "S 1"."T 1" t1, LATERAL (SELECT DISTINCT t2.c1, t3.c1 FROM ft1 t2, ft2 t3 WHERE t2.c1 = t3.c1 AND t2.c2 = t1.c2) q ORDER BY t1."C 1" OFFSET 10 LIMIT 10; SELECT t1."C 1" FROM "S 1"."T 1" t1, LATERAL (SELECT DISTINCT t2.c1, t3.c1 FROM ft1 t2, ft2 t3 WHERE t2.c1 = t3.c1 AND t2.c2 = t1.c2) q ORDER BY t1."C 1" OFFSET 10 LIMIT 10; +-- bug #15613: bad plan for foreign table scan with lateral reference +EXPLAIN (VERBOSE, COSTS OFF) +SELECT ref_0.c2, subq_1.* +FROM + "S 1"."T 1" AS ref_0, + LATERAL ( + SELECT ref_0."C 1" c1, subq_0.* + FROM (SELECT ref_0.c2, ref_1.c3 + FROM ft1 AS ref_1) AS subq_0 + RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3) + ) AS subq_1 +WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001' +ORDER BY ref_0."C 1"; + +SELECT ref_0.c2, subq_1.* +FROM + "S 1"."T 1" AS ref_0, + LATERAL ( + SELECT ref_0."C 1" c1, subq_0.* + FROM (SELECT ref_0.c2, ref_1.c3 + FROM ft1 AS ref_1) AS subq_0 + RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3) + ) AS subq_1 +WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001' +ORDER BY ref_0."C 1"; + -- non-Var items in targetlist of the nullable rel of a join preventing -- push-down in some cases -- unable to push {ft1, ft2} diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index f995a86e85..7656905da8 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -1855,6 +1855,29 @@ create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel, { ForeignPath *pathnode = makeNode(ForeignPath); + /* + * Since the path's required_outer should always include all the rel's + * lateral_relids, forcibly add those if necessary. This is a bit of a + * hack, but up till early 2019 the contrib FDWs failed to ensure that, + * and it's likely that the same error has propagated into many external + * FDWs. Don't risk modifying the passed-in relid set here. + */ + if (rel->lateral_relids && !bms_is_subset(rel->lateral_relids, + required_outer)) + required_outer = bms_union(required_outer, rel->lateral_relids); + + /* + * Although this function is only designed to be used for scans of + * baserels, before v12 postgres_fdw abused it to make paths for join and + * upper rels. It will work for such cases as long as required_outer is + * empty (otherwise get_baserel_parampathinfo does the wrong thing), which + * fortunately is the expected case for now. + */ + if (!bms_is_empty(required_outer) && + !(rel->reloptkind == RELOPT_BASEREL || + rel->reloptkind == RELOPT_OTHER_MEMBER_REL)) + elog(ERROR, "parameterized foreign joins are not supported yet"); + pathnode->path.pathtype = T_ForeignScan; pathnode->path.parent = rel; pathnode->path.pathtarget = target ? target : rel->reltarget; diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c index 23615f22e3..c8e94ab9fe 100644 --- a/src/backend/optimizer/util/relnode.c +++ b/src/backend/optimizer/util/relnode.c @@ -1002,6 +1002,9 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel, double rows; ListCell *lc; + /* If rel has LATERAL refs, every path for it should account for them */ + Assert(bms_is_subset(baserel->lateral_relids, required_outer)); + /* Unparameterized paths have no ParamPathInfo */ if (bms_is_empty(required_outer)) return NULL; @@ -1101,6 +1104,9 @@ get_joinrel_parampathinfo(PlannerInfo *root, RelOptInfo *joinrel, double rows; ListCell *lc; + /* If rel has LATERAL refs, every path for it should account for them */ + Assert(bms_is_subset(joinrel->lateral_relids, required_outer)); + /* Unparameterized paths have no ParamPathInfo or extra join clauses */ if (bms_is_empty(required_outer)) return NULL; @@ -1297,6 +1303,9 @@ get_appendrel_parampathinfo(RelOptInfo *appendrel, Relids required_outer) ParamPathInfo *ppi; ListCell *lc; + /* If rel has LATERAL refs, every path for it should account for them */ + Assert(bms_is_subset(appendrel->lateral_relids, required_outer)); + /* Unparameterized paths have no ParamPathInfo */ if (bms_is_empty(required_outer)) return NULL; -- 2.40.0