Subject: Re: The case when AsyncAppend exists also in the qual of Async
 ForeignScan
To: pgsql-bugs@lists.postgresql.org
References: <fe5eaa19-1704-e4a4-76ee-3b9d37ade399@postgrespro.ru>
 <CAPmGK170Y-6ysT1Vk+dmz4wXBq6Zq4+Sw2kMywsTdXduA0Svyw@mail.gmail.com>
 <9df9ea6b-75cb-27bd-79c3-b9145f97e7b3@postgrespro.ru>
 <CAPmGK17+CXJXs-+TGxqdzG=KKbOtiB5cWDSUKEMqfsFH2Lo-Gw@mail.gmail.com>
From: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
Organization: Postgres Professional
Message-ID: <bca32a14-3314-db8a-6b4f-97caa92aa214@postgrespro.ru>
Date: Tue, 27 Jul 2021 16:00:39 +0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: 
 <CAPmGK17+CXJXs-+TGxqdzG=KKbOtiB5cWDSUKEMqfsFH2Lo-Gw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Archived-At: 
 <https://www.postgresql.org/message-id/bca32a14-3314-db8a-6b4f-97caa92aa214%40postgrespro.ru>
Precedence: bulk

On 7/27/21 3:50 PM, Etsuro Fujita wrote:
> On Tue, Jul 27, 2021 at 3:22 PM Andrey V. Lepikhov
> <a.lepikhov@postgrespro.ru> wrote:
>>   >> Maybe we can split async logic into:
>>   >> - receiving stage, when we only fetch and store tuples,
>>   >> - evaluating stage, when we form resulting tuple and return by a
>>   >> scan node.
>>   >> I will think about such solution more.
> 
>>   > One simple solution along this line I came up with, which is not the
>>   > rewrite, is to 1) split process_pending_request() into the two steps,
>>   > and 2) postpone the second step until we are called from
>>   > postgresForeignAsyncConfigureWait(), like the attached, which I think
>>   > would be much consistent with the existing logic.
> 
>> Good idea. Are you planning to commit this patch?
> 
> Cool!
> 
> Here is an updated version of the patch, in which I added/tweaked
> comments a bit further.  I'm planning to push this version if there
> are no objections from others.
Thanks. In addition, I will use this patch in TPC-H benchmark tomorrow.
> 
>>   >> Also, may be you tell your opinion about an additional optimization
>>   >> of Async Append [1]?
> 
>>   > Is the optimization related to this issue?
> 
>> This optimization tries to postpone choice of async subplans. It allows
>> us to make a decision on async capable subplans after all plan
>> flattening operations.
> 
> Thanks for the explanation!  My understanding is that the optimization
> isn’t related to this issue.  Right?
Right

-- 
regards,
Andrey Lepikhov
Postgres Professional