[pgpool-general: 4076] Re: accept() scalability issues

Tatsuo Ishii ishii at postgresql.org
Fri Sep 25 19:04:57 JST 2015


Sorry for late reply.

>> On 25 Aug 2015, at 09:51, Tatsuo Ishii <ishii at postgresql.org> wrote:
>>> Thanks for the suggestion. Let me see how I can implement in other way
>>> using semtimedop().
> 
>> Here is the TPS from 3.3 stable head.
>> tps = 718.150625 (including connections establishing)
>> tps = 22368.793929 (excluding connections establishing)
>> 
>> So connection included TPS is ~700, connection excluded TPS is ~20000.
>> 
>> Here is the TPS from modified 3.3 stable (patch attached).
>> tps = 1999.094538 (including connections establishing)
>> tps = 13345.641707 (excluding connections establishing)
>> 
>> So connection included TPS is very good.  However connection time
>> excluded TPS is very low :-<
> 
> 
> Just to clarify, the difference between the runs including connection establishing and without is the “--connect” parameter to pgbench?

Yes.

> Seeing that your patch only modifies the code flow only for the accept loop, I see two options what could cause the slowdowns for the bench run using persistent connections.
> 
>  * Wakeups from timeouting children
> 
> Only 32 of the 400 children are used, in the past all the other children would block on select() and not wakeup, causing an undisturbed benchmark run. If ~360 children need to be woken up to complete their accept loop this might be a sufficient large interruption to affect the measurement

I believe this is a bug with pgbench. See my posting to pgsql-hackers
for more details.

http://www.postgresql.org/message-id/20150925.135347.2220251278958747939.t-ishii@sraoss.co.jp

> What was the setting of child_life_time?

30 seconds.

> * Load on the server
> 
> Seeing that you only did 10 seconds of benchmarking it could entirely be possible that something else interfered with your measurement.

I did longer a duration benchmarking but I didn't see much difference.

BTW I revisited "thundering herd problem" toward pgpool-II 3.5.
See my posting at pgpool-hackers.

http://www.pgpool.net/pipermail/pgpool-hackers/2015-September/001065.html

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp


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