Re: asynchronous execution

On 2017/03/14 10:08, Corey Huinker wrote:
>> I don't think the plan itself will change as a result of applying this
>> patch. You might however be able to observe some performance improvement.
>
> I could see no performance improvement, even with 16 separate queries
> combined with UNION ALL. Query performance was always with +/- 10% of a 9.6
> instance given the same script. I must be missing something.

Hmm, maybe I'm missing something too.

Anyway, here is an older message on this thread from Horiguchi-san where
he shared some of the test cases that this patch improves performance for:

https://www.postgresql.org/message-id/20161018.103051.30820907.horiguchi.kyotaro%40lab.ntt.co.jp

From that message:

<quote>
I measured performance and had the following result.

t0 - SELECT sum(a) FROM <local single table>;
pl - SELECT sum(a) FROM <4 local children>;
pf0 - SELECT sum(a) FROM <4 foreign children on single connection>;
pf1 - SELECT sum(a) FROM <4 foreign children on dedicate connections>;

The result is written as "time<ms> (std dev <ms>)"

sync
t0: 3820.33 ( 1.88)
pl: 1608.59 ( 12.06)
pf0: 7928.29 ( 46.58)
pf1: 8023.16 ( 26.43)

async
t0: 3806.31 ( 4.49) 0.4% faster (should be error)
pl: 1629.17 ( 0.29) 1.3% slower
pf0: 6447.07 ( 25.19) 18.7% faster
pf1: 1876.80 ( 47.13) 76.6% faster
</quote>

IIUC, pf0 and pf1 is the same test case (all 4 foreign tables target the
same server) measured with different implementations of the patch.

Thanks,
Amit