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
This commit is contained in:
Tom Lane
parent
b33d5e076e
commit
876fd37fc8
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@ -516,6 +516,10 @@ fileGetForeignPaths(PlannerInfo *root,
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* Create a ForeignPath node and add it as only possible path. We use the
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* fdw_private list of the path to carry the convert_selectively option;
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* it will be propagated into the fdw_private list of the Plan node.
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*
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* We don't support pushing join clauses into the quals of this path, but
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* it could still have required parameterization due to LATERAL refs in
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* its tlist.
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*/
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add_path(baserel, (Path *)
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create_foreignscan_path(root, baserel,
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@ -523,7 +527,7 @@ fileGetForeignPaths(PlannerInfo *root,
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startup_cost,
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total_cost,
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NIL, /* no pathkeys */
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NULL, /* no outer rel either */
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baserel->lateral_relids,
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coptions));
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/*
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@ -682,6 +682,62 @@ SELECT * FROM ft2 WHERE c1 = ANY (ARRAY(SELECT c1 FROM ft1 WHERE c1 < 5));
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4 | 4 | 00004 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4 | 4 | foo
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(4 rows)
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-- bug #15613: bad plan for foreign table scan with lateral reference
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT ref_0.c2, subq_1.*
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FROM
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"S 1"."T 1" AS ref_0,
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LATERAL (
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SELECT ref_0."C 1" c1, subq_0.*
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FROM (SELECT ref_0.c2, ref_1.c3
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FROM ft1 AS ref_1) AS subq_0
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RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3)
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) AS subq_1
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WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001'
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ORDER BY ref_0."C 1";
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QUERY PLAN
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---------------------------------------------------------------------------------------------------------
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Nested Loop
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Output: ref_0.c2, ref_0."C 1", (ref_0.c2), ref_1.c3, ref_0."C 1"
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-> Nested Loop
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Output: ref_0.c2, ref_0."C 1", ref_1.c3, (ref_0.c2)
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-> Index Scan using t1_pkey on "S 1"."T 1" ref_0
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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
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Index Cond: (ref_0."C 1" < 10)
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-> Foreign Scan on public.ft1 ref_1
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Output: ref_1.c3, ref_0.c2
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Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE ((c3 = '00001'::text))
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-> Materialize
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Output: ref_3.c3
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-> Foreign Scan on public.ft2 ref_3
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Output: ref_3.c3
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Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE ((c3 = '00001'::text))
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(15 rows)
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SELECT ref_0.c2, subq_1.*
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FROM
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"S 1"."T 1" AS ref_0,
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LATERAL (
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SELECT ref_0."C 1" c1, subq_0.*
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FROM (SELECT ref_0.c2, ref_1.c3
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FROM ft1 AS ref_1) AS subq_0
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RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3)
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) AS subq_1
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WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001'
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ORDER BY ref_0."C 1";
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c2 | c1 | c2 | c3
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----+----+----+-------
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1 | 1 | 1 | 00001
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2 | 2 | 2 | 00001
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3 | 3 | 3 | 00001
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4 | 4 | 4 | 00001
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5 | 5 | 5 | 00001
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6 | 6 | 6 | 00001
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7 | 7 | 7 | 00001
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8 | 8 | 8 | 00001
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9 | 9 | 9 | 00001
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(9 rows)
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-- ===================================================================
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-- parameterized queries
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-- ===================================================================
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@ -547,13 +547,16 @@ postgresGetForeignPaths(PlannerInfo *root,
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* baserestrict conditions we were able to send to remote, there might
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* actually be an indexscan happening there). We already did all the work
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* to estimate cost and size of this path.
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*
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* Although this path uses no join clauses, it could still have required
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* parameterization due to LATERAL refs in its tlist.
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*/
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path = create_foreignscan_path(root, baserel,
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fpinfo->rows,
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fpinfo->startup_cost,
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fpinfo->total_cost,
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NIL, /* no pathkeys */
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NULL, /* no outer rel either */
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baserel->lateral_relids,
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NIL); /* no fdw_private list */
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add_path(baserel, (Path *) path);
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@ -232,6 +232,32 @@ WHERE a.c2 = 6 AND b.c1 = a.c1 AND a.c8 = 'foo' AND b.c7 = upper(a.c7);
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SELECT * FROM ft1 WHERE c1 = ANY (ARRAY(SELECT c1 FROM ft2 WHERE c1 < 5));
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SELECT * FROM ft2 WHERE c1 = ANY (ARRAY(SELECT c1 FROM ft1 WHERE c1 < 5));
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-- bug #15613: bad plan for foreign table scan with lateral reference
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT ref_0.c2, subq_1.*
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FROM
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"S 1"."T 1" AS ref_0,
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LATERAL (
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SELECT ref_0."C 1" c1, subq_0.*
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FROM (SELECT ref_0.c2, ref_1.c3
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FROM ft1 AS ref_1) AS subq_0
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RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3)
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) AS subq_1
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WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001'
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ORDER BY ref_0."C 1";
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SELECT ref_0.c2, subq_1.*
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FROM
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"S 1"."T 1" AS ref_0,
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LATERAL (
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SELECT ref_0."C 1" c1, subq_0.*
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FROM (SELECT ref_0.c2, ref_1.c3
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FROM ft1 AS ref_1) AS subq_0
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RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3)
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) AS subq_1
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WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001'
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ORDER BY ref_0."C 1";
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-- ===================================================================
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-- parameterized queries
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-- ===================================================================
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@ -1736,6 +1736,29 @@ create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel,
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{
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ForeignPath *pathnode = makeNode(ForeignPath);
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/*
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* Since the path's required_outer should always include all the rel's
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* lateral_relids, forcibly add those if necessary. This is a bit of a
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* hack, but up till early 2019 the contrib FDWs failed to ensure that,
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* and it's likely that the same error has propagated into many external
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* FDWs. Don't risk modifying the passed-in relid set here.
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*/
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if (rel->lateral_relids && !bms_is_subset(rel->lateral_relids,
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required_outer))
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required_outer = bms_union(required_outer, rel->lateral_relids);
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/*
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* Although this function is only designed to be used for scans of
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* baserels, before v12 postgres_fdw abused it to make paths for join and
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* upper rels. It will work for such cases as long as required_outer is
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* empty (otherwise get_baserel_parampathinfo does the wrong thing), which
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* fortunately is the expected case for now.
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*/
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if (!bms_is_empty(required_outer) &&
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!(rel->reloptkind == RELOPT_BASEREL ||
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rel->reloptkind == RELOPT_OTHER_MEMBER_REL))
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elog(ERROR, "parameterized foreign joins are not supported yet");
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pathnode->path.pathtype = T_ForeignScan;
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pathnode->path.parent = rel;
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pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
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@ -857,6 +857,9 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
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double rows;
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ListCell *lc;
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/* If rel has LATERAL refs, every path for it should account for them */
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Assert(bms_is_subset(baserel->lateral_relids, required_outer));
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/* Unparameterized paths have no ParamPathInfo */
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if (bms_is_empty(required_outer))
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return NULL;
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@ -956,6 +959,9 @@ get_joinrel_parampathinfo(PlannerInfo *root, RelOptInfo *joinrel,
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double rows;
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ListCell *lc;
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/* If rel has LATERAL refs, every path for it should account for them */
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Assert(bms_is_subset(joinrel->lateral_relids, required_outer));
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/* Unparameterized paths have no ParamPathInfo or extra join clauses */
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if (bms_is_empty(required_outer))
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return NULL;
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@ -1152,6 +1158,9 @@ get_appendrel_parampathinfo(RelOptInfo *appendrel, Relids required_outer)
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ParamPathInfo *ppi;
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ListCell *lc;
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/* If rel has LATERAL refs, every path for it should account for them */
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Assert(bms_is_subset(appendrel->lateral_relids, required_outer));
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/* Unparameterized paths have no ParamPathInfo */
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if (bms_is_empty(required_outer))
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return NULL;
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