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Re: BUG #6296: High level backend-write activity on db

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Maksym Boguk <maxim(dot)boguk(at)gmail(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #6296: High level backend-write activity on db
Date: 2011-11-17 04:43:14
Message-ID: CA+TgmoZZ_UiFM9omaRhAsaAv+Sx6hzjcZS7tKHZzmtZfnx1wJw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On Wed, Nov 16, 2011 at 4:07 AM, Maksym Boguk <maxim(dot)boguk(at)gmail(dot)com> wrote:
> Again I not sure it is actual bug or something else go wrong with my
> database.
>
> One of my databases just started produce 256 wal segments in 5 minutes
> instead of 100-200 wal segments per hour (averages).
>
> In the same time write and read activity on DB stay same (according to the
> pg_stat_database data and historical graphs).
> No anti-wraparound vacuum and such things going on.
> Situation staying same during last few days.
>
>
> I found some other anomalies:
> 1)5 minutes after
> SELECT pg_stat_reset_shared('bgwriter');
>
> mirtesen=# SELECT * from pg_stat_bgwriter ;
>  checkpoints_timed | checkpoints_req | buffers_checkpoint | buffers_clean |
> maxwritten_clean | buffers_backend | buffers_alloc
> -------------------+-----------------+--------------------+---------------+-
> -----------------+-----------------+---------------
>                 0 |               2 |             171675 |           804 |
>              0 |         1010429 |       1131106
> (1 row)
>
> eg almost any new buffer allocated by backend leading to backend write out
> dirty page (and that situation do not change overtime).

This sure sounds like a ring buffer is being used, suggesting VACUUM
or COPY IN activity.

What does pg_stat_activity say?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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Subject: Re: BUG #6296: High level backend-write activity on db
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