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Ensure that foreign scans with lateral refs are planned correctly.

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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 2019-02-07 13:10:46 -05:00
parent 8722d2cbc0
commit 9d6d2b2134
6 changed files with 131 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
contrib/file_fdw/file_fdw.c
View File

@ -556,6 +556,10 @@ 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,
@ -564,7 +568,7 @@ fileGetForeignPaths(PlannerInfo *root,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no outer rel either */
baserel->lateral_relids,
NULL, /* no extra plan */
coptions));

56
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -3435,6 +3435,62 @@ select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum fr
(2 rows)
reset enable_hashagg;
-- 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)
-- Check with placeHolderVars
explain (verbose, costs off)
select sum(q.a), count(q.b) from ft4 left join (select 13, avg(ft1.c1), sum(ft2.c1) from ft1 right join ft2 on (ft1.c1 = ft2.c1)) q(a, b, c) on (ft4.c1 <= q.b);

18
contrib/postgres_fdw/postgres_fdw.c
View File

@ -930,6 +930,9 @@ 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 */
@ -937,7 +940,7 @@ 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);
@ -4978,7 +4981,7 @@ add_paths_with_pathkeys_for_rel(PlannerInfo *root, RelOptInfo *rel,
startup_cost,
total_cost,
useful_pathkeys,
NULL,
rel->lateral_relids,
sorted_epq_path,
NIL));
}
@ -5115,6 +5118,13 @@ 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
@ -5206,7 +5216,7 @@ postgresGetForeignJoinPaths(PlannerInfo *root,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no required_outer */
joinrel->lateral_relids,
epq_path,
NIL); /* no fdw_private */
@ -5534,7 +5544,7 @@ add_foreign_grouping_paths(PlannerInfo *root, RelOptInfo *input_rel,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no required_outer */
grouped_rel->lateral_relids,
NULL,
NIL); /* no fdw_private */

26
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -884,6 +884,32 @@ select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum fr
select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 3 and t1."C 1" < 100 order by 1;
reset enable_hashagg;
-- 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";
-- Check with placeHolderVars
explain (verbose, costs off)
select sum(q.a), count(q.b) from ft4 left join (select 13, avg(ft1.c1), sum(ft2.c1) from ft1 right join ft2 on (ft1.c1 = ft2.c1)) q(a, b, c) on (ft4.c1 <= q.b);

21
src/backend/optimizer/util/pathnode.c
View File

@ -2069,6 +2069,27 @@ 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) && !IS_SIMPLE_REL(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;

9
src/backend/optimizer/util/relnode.c
View File

@ -1247,6 +1247,9 @@ 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;
@ -1342,6 +1345,9 @@ 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;
@ -1533,6 +1539,9 @@ get_appendrel_parampathinfo(RelOptInfo *appendrel, Relids required_outer)
{
ParamPathInfo *ppi;
/* 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;