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* Migrating to 8.3 - checkpoints and background writer
@ 2007-11-05 00:33 Greg Smith <gsmith@gregsmith.com>
2007-11-05 00:39 ` Re: Migrating to 8.3 - checkpoints and background writer Steinar H. Gunderson <sgunderson@bigfoot.com>
2007-11-05 16:54 ` Re: Migrating to 8.3 - checkpoints and background writer Erik Jones <erik@myemma.com>
0 siblings, 2 replies; 4+ messages in thread
From: Greg Smith @ 2007-11-05 00:33 UTC (permalink / raw)
To: pgsql-performance
For those of you considering a move to the upcoming 8.3 release, now in
beta, I've written some documentation on the changes made in checkpoint
and background writer configuration in the new version:
http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm
Since the first half of that covers the current behavior in 8.1 and 8.2,
those sections may be helpful if you'd like to know more about checkpoint
slowdowns and ways to resolve them even if you have no plans to evaluate
8.3 yet. I'd certainly encourage anyone who can run the 8.3 beta to
consider adding some tests in this area while there's still time to
correct any issues encountered before the official release.
On the topic of performance improvements in 8.3, I don't think this list
has been getting information about the concurrent sequential scans
improvements. Check out these documents for more about that:
http://j-davis.com/postgresql/83v82_scans.html
http://j-davis.com/postgresql/syncscan/syncscan.pdf
http://j-davis.com/postgresql/syncscan/syncscan.odp
I particularly liked that first one because it gives a nice sample of how
to generate large amounts of data easily and then run benchmarks against
it, which is a handy thing to know for many types of performance
comparisons.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Migrating to 8.3 - checkpoints and background writer
2007-11-05 00:33 Migrating to 8.3 - checkpoints and background writer Greg Smith <gsmith@gregsmith.com>
@ 2007-11-05 00:39 ` Steinar H. Gunderson <sgunderson@bigfoot.com>
2007-11-05 03:06 ` Re: Migrating to 8.3 - checkpoints and background writer Greg Smith <gsmith@gregsmith.com>
1 sibling, 1 reply; 4+ messages in thread
From: Steinar H. Gunderson @ 2007-11-05 00:39 UTC (permalink / raw)
To: pgsql-performance
On Sun, Nov 04, 2007 at 07:33:46PM -0500, Greg Smith wrote:
> On the topic of performance improvements in 8.3, I don't think this list
> has been getting information about the concurrent sequential scans
> improvements. Check out these documents for more about that:
>
> http://j-davis.com/postgresql/83v82_scans.html
That's a nice writeup. I'm a bit puzzled by this part, though: "All tests
are on linux with the anticipatory I/O scheduler. The default I/O scheduler
for Linux is CFQ (Completely Fair Queue), which does not work well for
PostgreSQL in my tests."
All earlier benchmarks I've seen (even specifically for Postgres) have said
that cfq > deadline > anticipatory for database work. How large was the
difference for you?
/* Steinar */
--
Homepage: http://www.sesse.net/
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Migrating to 8.3 - checkpoints and background writer
2007-11-05 00:33 Migrating to 8.3 - checkpoints and background writer Greg Smith <gsmith@gregsmith.com>
2007-11-05 00:39 ` Re: Migrating to 8.3 - checkpoints and background writer Steinar H. Gunderson <sgunderson@bigfoot.com>
@ 2007-11-05 03:06 ` Greg Smith <gsmith@gregsmith.com>
0 siblings, 0 replies; 4+ messages in thread
From: Greg Smith @ 2007-11-05 03:06 UTC (permalink / raw)
To: pgsql-performance
On Mon, 5 Nov 2007, Steinar H. Gunderson wrote:
> I'm a bit puzzled by this part, though: "All tests are on linux with the
> anticipatory I/O scheduler. The default I/O scheduler for Linux is CFQ
> (Completely Fair Queue), which does not work well for PostgreSQL in my
> tests."
The syncronized scan articles were from Jeff Davis and I can't answer for
him. I will say I don't actually agree with that part of the document
myself and almost put a disclaimer to that effect in my message; here it
is now that you bring it up. I suspect the strong preference for avoiding
CFQ in his tests comes from the limitations of how simple (S)ATA drives
are handled in Linux, and that tests with a more robust disk subsystem may
very well give different results. Certainly the adaptive scheduler
appears stronger compared to CFQ as disk seek times go up, and that's the
area where regular hard drives are weakest relative to what's normally in
a server-class system.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Migrating to 8.3 - checkpoints and background writer
2007-11-05 00:33 Migrating to 8.3 - checkpoints and background writer Greg Smith <gsmith@gregsmith.com>
@ 2007-11-05 16:54 ` Erik Jones <erik@myemma.com>
1 sibling, 0 replies; 4+ messages in thread
From: Erik Jones @ 2007-11-05 16:54 UTC (permalink / raw)
To: Greg Smith <gsmith@gregsmith.com>; +Cc: pgsql-performance
On Nov 4, 2007, at 6:33 PM, Greg Smith wrote:
> For those of you considering a move to the upcoming 8.3 release,
> now in beta, I've written some documentation on the changes made in
> checkpoint and background writer configuration in the new version:
>
> http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm
>
> Since the first half of that covers the current behavior in 8.1 and
> 8.2, those sections may be helpful if you'd like to know more about
> checkpoint slowdowns and ways to resolve them even if you have no
> plans to evaluate 8.3 yet. I'd certainly encourage anyone who can
> run the 8.3 beta to consider adding some tests in this area while
> there's still time to correct any issues encountered before the
> official release.
Greg, thanks a lot of this. I'd say this should definitely be linked
to from the main site's techdocs section.
Erik Jones
Software Developer | Emma®
erik@myemma.com
800.595.4401 or 615.292.5888
615.292.0777 (fax)
Emma helps organizations everywhere communicate & market in style.
Visit us online at http://www.myemma.com
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-- links below jump to the message on this page --
2007-11-05 00:33 Migrating to 8.3 - checkpoints and background writer Greg Smith <gsmith@gregsmith.com>
2007-11-05 00:39 ` Steinar H. Gunderson <sgunderson@bigfoot.com>
2007-11-05 03:06 ` Greg Smith <gsmith@gregsmith.com>
2007-11-05 16:54 ` Erik Jones <erik@myemma.com>
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