Re: Push down more UPDATEs/DELETEs in postgres_fdw

Thanks Fujita-san for working on this. I've signed up to review this patch.

Your latest patch doesn't not get apply cleanly apply on master branch.

patching file contrib/postgres_fdw/deparse.c
6 out of 17 hunks FAILED -- saving rejects to file
contrib/postgres_fdw/deparse.c.rej
patching file contrib/postgres_fdw/expected/postgres_fdw.out
2 out of 2 hunks FAILED -- saving rejects to file
contrib/postgres_fdw/expected/postgres_fdw.out.rej
patching file contrib/postgres_fdw/postgres_fdw.c
2 out of 22 hunks FAILED -- saving rejects to file
contrib/postgres_fdw/postgres_fdw.c.rej
patching file contrib/postgres_fdw/postgres_fdw.h
1 out of 3 hunks FAILED -- saving rejects to file
contrib/postgres_fdw/postgres_fdw.h.rej

Please share the patch which get apply clean on master branch.

On Fri, Nov 11, 2016 at 5:00 PM, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
wrote:

> On 2016/09/08 19:55, Etsuro Fujita wrote:
>
>> On 2016/09/07 13:21, Ashutosh Bapat wrote:
>>
>>> * with the patch:
>>> postgres=# explain verbose delete from ft1 using ft2 where ft1.a =
>>> ft2.a;
>>> QUERY PLAN
>>>
>>> ------------------------------------------------------------
>>> -----------------------------------------------------------------
>>>
>>> Delete on public.ft1 (cost=100.00..102.04 rows=1 width=38)
>>> -> Foreign Delete (cost=100.00..102.04 rows=1 width=38)
>>> Remote SQL: DELETE FROM public.t1 r1 USING (SELECT ROW(a,
>>> b), a FROM public.t2) ss1(c1, c2) WHERE ((r1.a = ss1.c2))
>>> (3 rows)
>>>
>>
>> The underlying scan on t2 requires ROW(a,b) for locking the row for
>>> update/share. But clearly it's not required if the full query is being
>>> pushed down.
>>>
>>
> Is there a way we can detect that ROW(a,b) is useless
>>> column (not used anywhere in the other parts of the query like
>>> RETURNING, DELETE clause etc.) and eliminate it?
>>>
>>
> I don't have a clear solution for that yet, but I'll try to remove that
>> in the next version.
>>
>
> Similarly for a, it's
>>> part of the targetlist of the underlying scan so that the WHERE clause
>>> can be applied on it. But it's not needed if we are pushing down the
>>> query. If we eliminate the targetlist of the query, we could construct a
>>> remote query without having subquery in it, making it more readable.
>>>
>>
> Will try to do so also.
>>
>
> I addressed this by improving the deparse logic so that a remote query for
> performing an UPDATE/DELETE on a join directly on the remote can be created
> as proposed if possible. Attached is an updated version of the patch,
> which is created on top of the patch set [1]. The patch is still WIP (ie,
> needs more comments and regression tests, at least), but any comments would
> be gratefully appreciated.
>
> Best regards,
> Etsuro Fujita
>
> [1] https://www.postgresql.org/message-id/11eafd10-d3f8-ac8a-b64
> 2-b0e65037c76b%40lab.ntt.co.jp
>
>
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--
Rushabh Lathia