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From: David Fetter <david@fetter.org>
To: Andrew Dunstan <andrew@dunslane.net>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Daniel Farina <daniel@heroku.com>
Cc: Craig Ringer <ringerc@ringerc.id.au>
Cc: "Harold A. Giménez" <harold.gimenez@gmail.com>
Subject: Re: Checkpointer split has broken things dramatically (was Re: DELETE vs TRUNCATE explanation)
Date: Mon, 23 Jul 2012 05:41:23 -0700
Message-ID: <20120723124123.GA20499@fetter.org> (raw)
In-Reply-To: <500D439C.50608@dunslane.net>
References: <CA+Tgmoa4ta60Y-rZpEPDRCQKJV8-Uqe0P610Jgj2q7e+fondig@mail.gmail.com>
	<11952.1342456591@sss.pgh.pa.us>
	<CA+TgmoYRXMWQ_DGmmqu3Zp8oW3Lt-9Lc1q3EHaV_ZmjWqaPkuA@mail.gmail.com>
	<13011.1342457859@sss.pgh.pa.us>
	<CA+TgmoaEPLo5fmBX1JSkGK3umAamFVghwY7qDb4_QqzteZgUPA@mail.gmail.com>
	<15955.1342466333@sss.pgh.pa.us>
	<CA+TgmoYnqP!f03rYJo3G6dMrqShQF2iMtfpYBPgWdxtEdacaX-w@mail.gmail.com>
	<9247.1342565810@sss.pgh.pa.us>
	<20120723043733.GA13020@fetter.org>
	<500D439C.50608@dunslane.net>

On Mon, Jul 23, 2012 at 08:29:16AM -0400, Andrew Dunstan wrote:
> 
> On 07/23/2012 12:37 AM, David Fetter wrote:
> >On Tue, Jul 17, 2012 at 06:56:50PM -0400, Tom Lane wrote:
> >>Robert Haas <robertmhaas@gmail.com> writes:
> >>>On Mon, Jul 16, 2012 at 3:18 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >>>>BTW, while we are on the subject: hasn't this split completely
> >>>>broken the statistics about backend-initiated writes?
> >>>Yes, it seems to have done just that.
> >>This implies that nobody has done pull-the-plug testing on either
> >>HEAD or 9.2 since the checkpointer split went in (2011-11-01),
> >>because even a modicum of such testing would surely have shown that
> >>we're failing to fsync a significant fraction of our write traffic.
> >>
> >>Furthermore, I would say that any performance testing done since
> >>then, if it wasn't looking at purely read-only scenarios, isn't
> >>worth the electrons it's written on.  In particular, any performance
> >>gain that anybody might have attributed to the checkpointer splitup
> >>is very probably hogwash.
> >>
> >>This is not giving me a warm feeling about our testing practices.
> >Is there any part of this that the buildfarm, or some other automation
> >framework, might be able to handle?
> >
> 
> I'm not sure how you automate testing a pull-the-plug scenario.

I have a dim memory of how the FreeBSD project was alleged to have
done it, namely by rigging a serial port (yes, it was that long ago)
to the power supply of another machine and randomly cycling the power.

> The buildfarm is not at all designed to test performance. That's why
> we want a performance farm.

Right.  Apart from hardware, what are we stalled on?

Cheers,
David.
-- 
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david.fetter@gmail.com
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