Re: asynchronous execution

Hello. This is the final report in this CF period.

At Fri, 17 Mar 2017 17:35:05 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote in <20170317(dot)173505(dot)152063931(dot)horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
> Async-capable plan is generated in planner. An Append contains at
> least one async-capable child becomes async-aware Append. So the
> async feature should be effective also for the UNION ALL case.
>
> The following will work faster than unpatched version.I
>
> SELECT sum(a) FROM (SELECT a FROM ft10 UNION ALL SELECT a FROM ft20 UNION ALL SELECT a FROM ft30 UNION ALL SELECT a FROM ft40) as ft;
>
> I'll measure the performance for the case next week.

I found that the following query works as the same as partitioned
table.

SELECT sum(a) FROM (SELECT a FROM ft10 UNION ALL SELECT a FROM ft20 UNION ALL SELECT a FROM ft30 UNION ALL SELECT a FROM ft40 UNION ALL *SELECT a FROM ONLY pf0*) as ft;

So, the difference comes from the additional async-uncapable
child (faster if contains any). In both cases, Append node runs
children asynchronously but slightly differently when all
async-capable children are busy.

I'll continue working on this from this point aiming to the next
commit fest.

Thank you for valuable feedback.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center