Re: Trying to minimize the impact of checkpoints (resend)

There is something wonky on this mail list. I did not send this.


-----Original Message-----
From:    Gregory S. Williamson
Sent:    Fri 6/11/2004 2:10 PM
To:    jao@geophile.com
Cc:    pgsql-general@postgresql.org
Subject:    Re: [GENERAL] Trying to minimize the impact of checkpoints (resend)
In-reply-to: <1086983714.40ca0e22a9cb4@geophile.com>
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Comments: In-reply-to jao@geophile.commessage dated "Fri, 11 Jun 2004
    15:55:14 -0400"
Date: Fri, 11 Jun 2004 16:42:19 -0400
Message-ID: <18295.1086986539@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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jao@geophile.com writes:
> I'm using PostgreSQL 7.3.4 on RH9. Data and logs are on separate
> disks. (These are low-end IDE disks. That part of the problem
> is out of my control.)

> When a checkpoint occurs, all operations slow way, way down.

Not too surprising; you haven't got enough I/O bandwidth.

> Does anyone have any experience in modifying the priority of the
> checkpoint process itself, (re-nicing it)?

That would be a waste of time, because your problem is with I/O usage
not CPU usage, and nice doesn't impact I/O scheduling AFAIK.

You might be able to get somewhere by inserting intrapage delays into
the checkpoint write loop, similar to what's been done to VACUUM since
7.4.  (I have a todo item to do this for CVS tip, in fact.)  You'd not
want this to happen during a shutdown checkpoint, but for ordinary
checkpoints I don't believe there's any problem with spacing out the
writes.

            regards, tom lane

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