Subject: Re: Asynchronous Append on postgres_fdw nodes.
To: Etsuro Fujita <etsuro.fujita@gmail.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
 Justin Pryzby <pryzby@telsasoft.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
References: 
 <CAPmGK14igABfEruPPh1X=9KnjY=LquRHQij48oATSo1vWr7yOg@mail.gmail.com>
 <CAPmGK15xtFk2gb9-2b24mFtYBVWoGkmCPFPkM9RHpKVXGLk=sw@mail.gmail.com>
 <CAPmGK178d9-+aFgYorOY4n0pZmZ55WpQ7i1JcCagovYzAh+ueg@mail.gmail.com>
 <20210331.101137.148208859959175708.horikyota.ntt@gmail.com>
 <CAPmGK17T9Swy2FHZk4AVVKNzRxVnd96PX-18DSC2jeDXWNiBoQ@mail.gmail.com>
 <CAPmGK1637W30Wx3MnrReewhafn6F_0J76mrJGoFXFnpPq4QfvA@mail.gmail.com>
 <CAPmGK17O6fMfX84wWfypLWAO4NvD4fgDhm--oyzZ97YP+TxckA@mail.gmail.com>
 <c9388cb7-8cfc-bc92-0d6a-b519e6099cb6@postgrespro.ru>
 <CAPmGK17JTeGJtKrW_xeRtbXaPBBEQy3+AcOdqcrM0fnHGmJVsw@mail.gmail.com>
From: Andrey Lepikhov <a.lepikhov@postgrespro.ru>
Organization: Postgres Professional
Message-ID: <52d944ea-7d41-1d16-01b7-8d1edf5ea972@postgrespro.ru>
Date: Fri, 7 May 2021 15:35:50 +0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0)
 Gecko/20100101 Thunderbird/78.10.1
MIME-Version: 1.0
In-Reply-To: 
 <CAPmGK17JTeGJtKrW_xeRtbXaPBBEQy3+AcOdqcrM0fnHGmJVsw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Archived-At: 
 <https://www.postgresql.org/message-id/52d944ea-7d41-1d16-01b7-8d1edf5ea972%40postgrespro.ru>
Precedence: bulk

On 6/5/21 14:11, Etsuro Fujita wrote:
> On Tue, Apr 27, 2021 at 3:57 PM Andrey V. Lepikhov
> <a.lepikhov@postgrespro.ru> wrote:
>> One more question. Append choose async plans at the stage of the Append
>> plan creation.
>> Later, the planner performs some optimizations, such as eliminating
>> trivial Subquery nodes. So, AsyncAppend is impossible in some
>> situations, for example:
>>
>> (SELECT * FROM f1 WHERE a < 10)
>>     UNION ALL
>> (SELECT * FROM f2 WHERE a < 10);
>>
>> But works for the query:
>>
>> SELECT *
>>     FROM (SELECT * FROM f1 UNION ALL SELECT * FROM f2) AS q1
>> WHERE a < 10;
>>
>> As far as I understand, this is not a hard limit.
> 
> I think so, but IMO I think this would be an improvement rather than a bug fix.
> 
>> We can choose async
>> subplans at the beginning of the execution stage.
>> For a demo, I prepared the patch (see in attachment).
>> It solves the problem and passes the regression tests.
> 
> Thanks for the patch!  IIUC, another approach to this would be the
> patch you proposed before [1].  Right?
Yes. I think, new solution will be better.

-- 
regards,
Andrey Lepikhov
Postgres Professional