Re: Add semi-join pushdown to postgres_fdw

2022年8月30日(火) 15:58 Alexander Pyhalov <a.pyhalov@postgrespro.ru>:
>
> Ashutosh Bapat писал 2022-08-29 17:12:
> > Hi Alexander,
> > Thanks for working on this. It's great to see FDW join pushdown scope
> > being expanded to more complex cases.
> >
> > I am still figuring out the implementation. It's been a while I have
> > looked at join push down code.
> >
> > But following change strikes me odd
> >  -- subquery using immutable function (can be sent to remote)
> >  PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3
> > IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) =
> > '1970-01-17'::date) ORDER BY c1;
> >  EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
> > -                                                      QUERY PLAN
> >
------------------------------------------------------------------------------------------------------------------------
> > - Sort
> > +
> >
> > QUERY PLAN
> >
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> > + Foreign Scan
> >     Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
> > -   Sort Key: t1.c1
> > -   ->  Nested Loop Semi Join
> > -         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7,
> > t1.c8
> > -         Join Filter: (t1.c3 = t2.c3)
> > -         ->  Foreign Scan on public.ft1 t1
> > -               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6,
> > t1.c7, t1.c8
> > -               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8
> > FROM "S 1"."T 1" WHERE (("C 1" < 20))
> > -         ->  Materialize
> > -               Output: t2.c3
> > -               ->  Foreign Scan on public.ft2 t2
> > -                     Output: t2.c3
> > -                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE
> > (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
> > -(14 rows)
> > +   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
> > +   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6,
> > r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND (EXISTS
> > (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND
> > ((date(r3.c5) = '1970-01-17'::date)) AND ((r1.c3 = r3.c3)))) ORDER BY
> > r1."C 1" ASC NULLS LAST
> > +(4 rows)
> >
> > date_in              | s           |        1 | [0:0]={cstring}
> > date_in which will be used to cast a test to date is not immutable. So
> > the query should't be pushed down. May not be a problem with your
> > patch. Can you please check?
>
> Hi.
>
> It is not related to my change and works as expected. As I see, we have
> expression FuncExprdate(oid = 2029, args=Var ) = Const(type date)
> (date(r3.c5) = '1970-01-17'::date).
> Function is
>
> # select proname, provolatile from pg_proc where oid=2029;
>   proname | provolatile
> ---------+-------------
>   date    | i
>
> So it's shippable.

This entry was marked as "Needs review" in the CommitFest app but cfbot
reports the patch no longer applies.

We've marked it as "Waiting on Author". As CommitFest 2022-11 is
currently underway, this would be an excellent time update the patch.

Once you think the patchset is ready for review again, you (or any
interested party) can  move the patch entry forward by visiting

    https://commitfest.postgresql.org/40/3838/

and changing the status to "Needs review".


Thanks

Ian Barwick