Hi,
While reviewing the foreign join pushdown core patch, I noticed that the
patch doesn't perform an EvalPlanQual recheck properly. The example
that crashes the server will be shown below (it uses the postgres_fdw
patch [1]). I think the reason for that is because the ForeignScan node
performing the foreign join remotely has scanrelid = 0 while
ExecScanFetch assumes that its scan node has scanrelid > 0.
I think this is a bug. I've not figured out how to fix this yet, but I
thought we would also need another plan that evaluates the join locally
for the test tuples for EvalPlanQual. Though I'm missing something though.
Create an environment:
postgres=# create table tab (a int, b int);
CREATE TABLE
postgres=# create foreign table foo (a int) server myserver options
(table_name 'foo');
CREATE FOREIGN TABLE
postgres=# create foreign table bar (a int) server myserver options
(table_name 'bar');
CREATE FOREIGN TABLE
postgres=# insert into tab values (1, 1);
INSERT 0 1
postgres=# insert into foo values (1);
INSERT 0 1
postgres=# insert into bar values (1);
INSERT 0 1
postgres=# analyze tab;
ANALYZE
postgres=# analyze foo;
ANALYZE
postgres=# analyze bar;
ANALYZE
Run the example:
[Terminal 1]
postgres=# begin;
BEGIN
postgres=# update tab set b = b + 1 where a = 1;
UPDATE 1
[Terminal 2]
postgres=# explain verbose select tab.* from tab, foo, bar where tab.a =
foo.a and foo.a = bar.a for update;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------
LockRows (cost=100.00..101.18 rows=4 width=70)
Output: tab.a, tab.b, tab.ctid, foo.*, bar.*
-> Nested Loop (cost=100.00..101.14 rows=4 width=70)
Output: tab.a, tab.b, tab.ctid, foo.*, bar.*
Join Filter: (foo.a = tab.a)
-> Seq Scan on public.tab (cost=0.00..1.01 rows=1 width=14)
Output: tab.a, tab.b, tab.ctid
-> Foreign Scan (cost=100.00..100.08 rows=4 width=64)
Output: foo.*, foo.a, bar.*, bar.a
Relations: (public.foo) INNER JOIN (public.bar)
Remote SQL: SELECT l.a1, l.a2, r.a1, r.a2 FROM (SELECT
ROW(l.a9), l.a9 FROM (SELECT a a9 FROM public.foo FOR UPDATE) l) l (a1,
a2) INNER
JOIN (SELECT ROW(r.a9), r.a9 FROM (SELECT a a9 FROM public.bar FOR
UPDATE) r) r (a1, a2) ON ((l.a2 = r.a2))
(11 rows)
postgres=# select tab.* from tab, foo, bar where tab.a = foo.a and foo.a
= bar.a for update;
[Terminal 1]
postgres=# commit;
COMMIT
[Terminal 2]
(After the commit in Terminal 1, Terminal 2 will show the following.)
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>
Best regards,
Etsuro Fujita
[1]
http://www.postgresql.org/message-id/CAEZqfEe9KGy=1_wagh2rgzpg0o4pqgd+iauyaj8wtze+cyj...@mail.gmail.com
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