From: Greg Smith <gsmith@gregsmith.com>
To: Laurent Wandrebeck <l.wandrebeck@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: "iowait" bug?
Date: Mon, 23 Mar 2009 00:04:40 -0400 (EDT)
Message-ID: <alpine.GSO.2.01.0903222356240.7558@westnet.com> (raw)
In-Reply-To: <fc593b510903221614p40fcb271o17ad937c4968ade2@mail.gmail.com>
References: <af0420cd0903200945m7f70d057p12942b50c8266bcb@mail.gmail.com>
<af0420cd0903202117i66109820s31b440bc7648c358@mail.gmail.com>
<alpine.GSO.2.01.0903221507500.8979@westnet.com>
<fc593b510903221614p40fcb271o17ad937c4968ade2@mail.gmail.com>
On Mon, 23 Mar 2009, Laurent Wandrebeck wrote:
> I thought about completely fair scheduler at first, but that one came
> in around 2.6.21.
CFS showed up in 2.6.23.
> I think that forcing the system to write down more often, and smaller
> data just hides the problem, and doesn't correct it.
That's one possibility. I've been considering things like whether the OS
is getting bogged down managing things like the elevator sorting for
outstanding writes. If there was something about that process that gets
really inefficient proportionally to the size of the pending queue, that
would both match the kinds of symptoms people are reporting, and would go
better just reducing the maximum size of the issue by lowering the pdflush
tunables.
Anyway, the point I was trying to make is that there sure seem to be
multiple problems mixed into that one bug report, and it's starting to
look just as unmanagably messy as the older bug that had to be abandoned.
It would have been nice if somebody kicked out all the diversions it
wanted into to keep the focus a bit better. Anybody using a SSD device,
USB, or ext4 should have been punted to somewhere else for example.
Plenty of examples that don't require any of those things.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: gsmith@gregsmith.com, l.wandrebeck@gmail.com
Subject: Re: "iowait" bug?
In-Reply-To: <alpine.GSO.2.01.0903222356240.7558@westnet.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox