From: Alex Deucher <alexdeucher@gmail.com>
To: Ron <rjpeace@earthlink.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: strange performance regression between 7.4 and 8.1
Date: Fri, 2 Mar 2007 16:20:41 -0500
Message-ID: <a728f9f90703021320rddfaa88wbb315ef86547aaee@mail.gmail.com> (raw)
In-Reply-To: <E1HNEMf-00060s-4C@elasmtp-banded.atl.sa.earthlink.net>
References: <a728f9f90703011244r577d56d7y422ab4bd71bb760e@mail.gmail.com>
<82slco6n9t.fsf@mid.bfk.de>
<a728f9f90703020716g45b2d281u9894973abad3e68a@mail.gmail.com>
<E1HN9zd-0001tV-Gi@elasmtp-galgo.atl.sa.earthlink.net>
<a728f9f90703020803r2ab76789sa63def90642fe5c@mail.gmail.com>
<E1HNC2e-0005Cl-II@elasmtp-scoter.atl.sa.earthlink.net>
<a728f9f90703021143l2da54eb1r61d4fe7609629b17@mail.gmail.com>
<E1HNEMf-00060s-4C@elasmtp-banded.atl.sa.earthlink.net>
On 3/2/07, Ron <rjpeace@earthlink.net> wrote:
> At 02:43 PM 3/2/2007, Alex Deucher wrote:
> >On 3/2/07, Ron <rjpeace@earthlink.net> wrote:
> >>
> >>...and I still think looking closely at the actual physical layout of
> >>the tables in the SAN is likely to be worth it.
> >
> >How would I go about doing that?
> >
> >Alex
>
> Hard for me to give specific advice when I don't know what SAN
> product we are talking about nor what kind of HDs are in it nor how
> those HDs are presently configured...
>
> I quote you in an earlier post:
> "The RAID groups on the SAN were set up for maximum capacity rather
> than for performance. Using it for the databases just came up recently."
>
> That implies to me that the SAN is more or less set up as a huge 105
> HD (assuming this number is correct? We all know how "assume" is
> spelled...) JBOD or RAID 5 (or 6, or 5*, or 6*) set.
>
> =IF= that is true, tables are not being given dedicated RAID
> groups. That implies that traditional lore like having pg_xlog on
> dedicated spindles is being ignored.
> Nor is the more general Best Practice of putting the most heavily
> used tables onto dedicated spindles being followed.
>
> In addition, the most space efficient RAID levels: 5* or 6*, are not
> the best performing one (RAID 10 striping your mirrors)
>
> In short, configuring a SAN for maximum capacity is exactly the wrong
> thing to do if one is planning to use it in the best way to support
> DB performance.
>
> I assume (there's that word again...) that there is someone in your
> organization who understands how the SAN is configured and administered.
> You need to talk to them about these issues.
>
Ah OK. I see what you are saying; thank you for clarifying. Yes,
the SAN is configured for maximum capacity; it has large RAID 5
groups. As I said earlier, we never intended to run a DB on the SAN,
it just happened to come up, hence the configuration.
Alex
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: alexdeucher@gmail.com, rjpeace@earthlink.net
Subject: Re: strange performance regression between 7.4 and 8.1
In-Reply-To: <a728f9f90703021320rddfaa88wbb315ef86547aaee@mail.gmail.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