Re: The case when AsyncAppend exists also in the qual of Async ForeignScan

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