Message-ID: <535EC5CC.5090504@fuzzy.cz>
Date: Mon, 28 Apr 2014 23:19:08 +0200
From: Tomas Vondra <tv@fuzzy.cz>
User-Agent: Mozilla/5.0 (X11; Linux x86_64;
 rv:24.0) Gecko/20100101 Thunderbird/24.4.0
MIME-Version: 1.0
To: Jeff Janes <jeff.janes@gmail.com>
CC: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: Checkpoints and slow queries
References: 
 <CALqA5kjzDQ2X1Am5zNjg3R5vCmZD-D0_6nrO1ccVD8vOmej22g@mail.gmail.com>
	<535D88B6.5090002@fuzzy.cz>
	<CALqA5kgoni52uqsSDeZStXZReXdpzGtSQ8iTtHbmx5oKOb1G6Q@mail.gmail.com>
	<10039.1398694057@sss.pgh.pa.us>	<535EBCEC.4000501@fuzzy.cz>
 <CAMkU=1xym__n4hg-AfzKhimDzWQtUjJAMWcXX05LAbwJfuxJDQ@mail.gmail.com>
In-Reply-To: 
 <CAMkU=1xym__n4hg-AfzKhimDzWQtUjJAMWcXX05LAbwJfuxJDQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

On 28.4.2014 22:54, Jeff Janes wrote:
> On Mon, Apr 28, 2014 at 1:41 PM, Tomas Vondra <tv@fuzzy.cz
>     There's certainly something fishy, because although this is the supposed
>     configuration:
> 
>     checkpoint_segments = 250
>     checkpoint_timeout = 1h
>     checkpoint_completion_target = 0.9
> 
>     the checkpoint logs typically finish in much shorter periods of time.
> 
> That doesn't look fishy to me.  The checkpointer will not take more than
> one nap between buffers, so it will always write at least 10 buffers per
> second (of napping time) even if that means it finishes early.  Which
> seems to be the case here--the length of the write cycle seems to be
> about one tenth the number of buffers written.

Oh, makes sense I guess. Apparently I'm tuning this only on systems
doing a lot of I/O, so this behaviour somehow escaped me.

Tomas


-- 
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance