Re: bgwriter tunables vs pg_stat_bgwriter

От: Brad Nicholson
Тема: Re: bgwriter tunables vs pg_stat_bgwriter
Дата: ,
Msg-id: 1266433276.4412.39.camel@bnicholson-desktop
(см: обсуждение, исходный текст)
Ответ на: bgwriter tunables vs pg_stat_bgwriter  (Jeff)
Список: pgsql-performance

Скрыть дерево обсуждения

bgwriter tunables vs pg_stat_bgwriter  (Jeff, )
 Re: bgwriter tunables vs pg_stat_bgwriter  (Brad Nicholson, )
 Re: bgwriter tunables vs pg_stat_bgwriter  (Greg Smith, )
  Re: bgwriter tunables vs pg_stat_bgwriter  (Jeff, )

On Wed, 2010-02-17 at 08:30 -0500, Jeff wrote:
> Since getting on 8.4 I've been monitoring things fairly closely.
> I whipped up a quick script to monitor pg_stat_bgwriter and save
> deltas every minute so I can ensure my bgwriter is beating out the
> backends for writes (as it is supposed to do).
>
> Now, the odd thing I'm running into is this:
>
> bgwriter_delay is 100ms (ie 10 times a second, give or take)
> bgwriter_lru_maxpages is 500 (~5000 pages / second)
> bgwriter_lru_multiplier is 4
>
> Now, assuming I understand these values right the following is what
> should typically happen:
>
> while(true)
> {
>      if buffers_written > bgwriter_lru_maxpages
>        or buffers_written > anticipated_pages_needed *
> bgwriter_lru_multiplier
>     {
>           sleep(bgwriter_delay ms)
>            continue;
>     }
>     ...
> }

Correct.

> so I should not be able to have more than ~5000 bgwriter_clean pages
> per minute. (this assumes writing takes 0ms, which of course is
> inaccurate)

That works out to 5000/second - 300,000/minute.

> However, I see this in my stats (they are deltas), and I'm reasonably
> sure it is not a bug in the code:
>
> (timestamp, buffers clean, buffers_checkpoint, buffers backend)
>   2010-02-17 08:23:51.184018 |             1 |               1686
> |               5
>   2010-02-17 08:22:51.170863 |         15289 |              12676
> |             207
>   2010-02-17 08:21:51.155793 |         38467 |               8993
> |            4277
>   2010-02-17 08:20:51.139199 |         35582 |                  0
> |            9437
>   2010-02-17 08:19:51.125025 |             8 |                  0
> |               3
>   2010-02-17 08:18:51.111184 |          1140 |               1464
> |               6
>   2010-02-17 08:17:51.098422 |             0 |               1682
> |             228
>   2010-02-17 08:16:51.082804 |            50 |                  0
> |               6
>   2010-02-17 08:15:51.067886 |           789 |                  0
> |               1
>
> perhaps some stats buffering occurring or something or some general
> misunderstanding of some of these tunables?
>
> --
> Jeff Trout <>
> http://www.stuarthamm.net/
> http://www.dellsmartexitin.com/
>
>
>
>
--
Brad Nicholson  416-673-4106
Database Administrator, Afilias Canada Corp.




В списке pgsql-performance по дате сообщения:

От: Michael Clemmons
Дата:
Сообщение: Michael Clemmons wants to stay in touch on LinkedIn
От: AI Rumman
Дата:
Сообщение: index usage in not like