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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
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56
contrib/postgres_fdw/expected/postgres_fdw.out
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@ -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);