We are running PostgreSQL as the back-end to a spam scanning system. The
database holds suspected spam, and user configuration information. A
web interface allows people to accept, or (usually) discard the trapped
messages. So, most data is write once, read at most once, delete.

The total size of the db is about 16gig in size. And, we expect it
could grow to 4 times this as more users are opted into spam scanning.
During most of the day, the machine is only lightly loaded. There are
two bursts of activity: the nightly vacuum, and the first thing in the
morning spam checking.

Our current db machine has two hyper-threaded 2.4 GHz Xeon processors, 4
gig of main memory, and is attached to a JBOD configured with RAID 5 for
the database, and mirrored disks for the DB logs.

It is time to upgrade the machine. Two possibilities present themselves.

1. PowerEdge 6850
4 3.16 GHz Xeon processors
16 gig of memory
Internal RAID 5 (only 3 disks)
2 Mirrored disks for root and db log.

2. PowerEdge 2850
2 Dual core 2.8GHz Xeon processors
8 gig of memory
JBOD with RAID 5, and mirrored db log.

Both configurations will cost about the same, within $\Delta$ for an
acceptable value of $\Delta$. The idea behind the first is to keep the
entire database in memory, by way of the disk cache. Alas, to keep it
affordable (The extra memory is expensive) the JBOD must be jettisoned.
The second is a larger version of our current configuration. (The 6850
with a JBOD would stretch the budget beyond $\Delta$, and the expense
would be difficult to justify.)

I'm looking for any comments, or suggestions. With expected growth, the
first configuration seems out of balance---it will likely start off
fast, but with growth the slower disk configuration will likely be a
problem. Is anybody running PostgreSQL in a large memory, slower disk
configuration? What are your experiences.

Thank You,

Mike

P.S. We are investigating if the current IBM JBOD will work with the
Dell PERC cards. But, even if they do, the current JBOD is populated
with soon to be extended warranty disks, and so progressively costly.

--
Michael D. Sofka sofkam@rpi.edu
C&CT Sr. Systems Programmer Email, TeX, epistemology.
Rensselaer Polytechnic Institute, Troy, NY. http://www.rpi.edu/~sofkam/


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TIP 6: explain analyze is your friend

Two general comments: most people find that Opterons perform much better
than Xeons. With some versions of PostgreSQL, the difference is over
50%.

RAID5 generally doesn't make for a fast database. The problem is that
there is a huge amount of overhead everytime you go to write something
out to a RAID5 array. With careful tuning of the background writer you
might be able to avoid some of that penalty, though your read
performance will likely still be affected by the write overhead.

BTW, -performance is a better list for info about this. If you look in
the archives you'll be able to read a lot of threads from people seeking
hardware advice.

On Thu, Nov 17, 2005 at 09:54:38AM -0500, Michael D. Sofka wrote:
> We are running PostgreSQL as the back-end to a spam scanning system. The
> database holds suspected spam, and user configuration information. A
> web interface allows people to accept, or (usually) discard the trapped
> messages. So, most data is write once, read at most once, delete.
>
> The total size of the db is about 16gig in size. And, we expect it
> could grow to 4 times this as more users are opted into spam scanning.
> During most of the day, the machine is only lightly loaded. There are
> two bursts of activity: the nightly vacuum, and the first thing in the
> morning spam checking.
>
> Our current db machine has two hyper-threaded 2.4 GHz Xeon processors, 4
> gig of main memory, and is attached to a JBOD configured with RAID 5 for
> the database, and mirrored disks for the DB logs.
>
> It is time to upgrade the machine. Two possibilities present themselves.
>
> 1. PowerEdge 6850
> 4 3.16 GHz Xeon processors
> 16 gig of memory
> Internal RAID 5 (only 3 disks)
> 2 Mirrored disks for root and db log.
>
> 2. PowerEdge 2850
> 2 Dual core 2.8GHz Xeon processors
> 8 gig of memory
> JBOD with RAID 5, and mirrored db log.
>
> Both configurations will cost about the same, within $\Delta$ for an
> acceptable value of $\Delta$. The idea behind the first is to keep the
> entire database in memory, by way of the disk cache. Alas, to keep it
> affordable (The extra memory is expensive) the JBOD must be jettisoned.
> The second is a larger version of our current configuration. (The 6850
> with a JBOD would stretch the budget beyond $\Delta$, and the expense
> would be difficult to justify.)
>
> I'm looking for any comments, or suggestions. With expected growth, the
> first configuration seems out of balance---it will likely start off
> fast, but with growth the slower disk configuration will likely be a
> problem. Is anybody running PostgreSQL in a large memory, slower disk
> configuration? What are your experiences.
>
> Thank You,
>
> Mike
>
> P.S. We are investigating if the current IBM JBOD will work with the
> Dell PERC cards. But, even if they do, the current JBOD is populated
> with soon to be extended warranty disks, and so progressively costly.
>
> --
> Michael D. Sofka sofkam@rpi.edu
> C&CT Sr. Systems Programmer Email, TeX, epistemology.
> Rensselaer Polytechnic Institute, Troy, NY. http://www.rpi.edu/~sofkam/
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>

--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461

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TIP 5: don't forget to increase your free space map settings

On Sun, 2005-11-20 at 11:53 -0600, Jim C. Nasby wrote:
> Two general comments: most people find that Opterons perform much better
> than Xeons. With some versions of PostgreSQL, the difference is over
> 50%.

Could you be more specific on that? Which version of Postgres perform
better on Opteron than on Xeon?

> RAID5 generally doesn't make for a fast database. The problem is that
> there is a huge amount of overhead everytime you go to write something
> out to a RAID5 array. With careful tuning of the background writer you
> might be able to avoid some of that penalty, though your read
> performance will likely still be affected by the write overhead.

RAID5 was not ment to improve performance, but to minimize disaster and
downtime when your hard disk dies. We're using RAID5 with postgres. In
the last 3 years we changed 5 disks, but the system downtime was zero
minutes.


Mike
--
Mario Splivalo
Mob-Art
mario.splivalo@mobart.hr

"I can do it quick, I can do it cheap, I can do it well. Pick any two."



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TIP 4: Have you searched our list archives?

http://archives.postgresql.org

Dnia poniedzia³ek, 21 listopada 2005 10:34, Mario Splivalo napisa³:
> On Sun, 2005-11-20 at 11:53 -0600, Jim C. Nasby wrote:
> > Two general comments: most people find that Opterons perform much better
> > than Xeons. With some versions of PostgreSQL, the difference is over
> > 50%.
>
> Could you be more specific on that? Which version of Postgres perform
> better on Opteron than on Xeon?

Try http://85.128.68.44 - I made some test about Xeon and Opteron

>
> > RAID5 generally doesn't make for a fast database. The problem is that
> > there is a huge amount of overhead everytime you go to write something
> > out to a RAID5 array. With careful tuning of the background writer you
> > might be able to avoid some of that penalty, though your read
> > performance will likely still be affected by the write overhead.
>
> RAID5 was not ment to improve performance, but to minimize disaster and
> downtime when your hard disk dies. We're using RAID5 with postgres. In
> the last 3 years we changed 5 disks, but the system downtime was zero
> minutes.

I'm ready enough to put some tests about different RAID's for Postgresql - but
I will soon. However almost all people I know preffer RAID10 for database
like PGSQL.

Marcin

>
>
> Mike

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On Mon, 2005-11-21 at 10:58 +0100, Marcin Giedz wrote:
> Dnia poniedziałek, 21 listopada 2005 10:34, Mario Splivalo napisał:
> > On Sun, 2005-11-20 at 11:53 -0600, Jim C. Nasby wrote:
> > > Two general comments: most people find that Opterons perform much better
> > > than Xeons. With some versions of PostgreSQL, the difference is over
> > > 50%.
> >
> > Could you be more specific on that? Which version of Postgres perform
> > better on Opteron than on Xeon?
>
> Try http://85.128.68.44 - I made some test about Xeon and Opteron

Cool! Could you give specs on processors itself? The clock, cache,
and stuff?

> > RAID5 was not ment to improve performance, but to minimize disaster and
> > downtime when your hard disk dies. We're using RAID5 with postgres. In
> > the last 3 years we changed 5 disks, but the system downtime was zero
> > minutes.
>
> I'm ready enough to put some tests about different RAID's for Postgresql - but
> I will soon. However almost all people I know preffer RAID10 for database
> like PGSQL.

What do you mean when you say RAID10? Raid 1+0, or striped raid 5?

Mike
--
Mario Splivalo
Mob-Art
mario.splivalo@mobart.hr

"I can do it quick, I can do it cheap, I can do it well. Pick any two."



---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
subscribe-nomail command to majordomo@postgresql.org so that your
message can get through to the mailing list cleanly

Dnia poniedziałek, 21 listopada 2005 11:23, Mario Splivalo napisał:
> On Mon, 2005-11-21 at 10:58 +0100, Marcin Giedz wrote:
> > Dnia poniedziałek, 21 listopada 2005 10:34, Mario Splivalo napisał:
> > > On Sun, 2005-11-20 at 11:53 -0600, Jim C. Nasby wrote:
> > > > Two general comments: most people find that Opterons perform much
> > > > better than Xeons. With some versions of PostgreSQL, the difference
> > > > is over 50%.
> > >
> > > Could you be more specific on that? Which version of Postgres perform
> > > better on Opteron than on Xeon?
> >
> > Try http://85.128.68.44 - I made some test about Xeon and Opteron
>
> Cool! Could you give specs on processors itself? The clock, cache,
> and stuff?

Look at this site once again - made some additional info.

>
> > > RAID5 was not ment to improve performance, but to minimize disaster and
> > > downtime when your hard disk dies. We're using RAID5 with postgres. In
> > > the last 3 years we changed 5 disks, but the system downtime was zero
> > > minutes.
> >
> > I'm ready enough to put some tests about different RAID's for Postgresql
> > - but I will soon. However almost all people I know preffer RAID10 for
> > database like PGSQL.
>
> What do you mean when you say RAID10? Raid 1+0, or striped raid 5?

Raid 1+0.


>
> Mike

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Marcin Giedz wrote:
> Dnia poniedzia??ek, 21 listopada 2005 16:31, Alvaro Herrera napisa??:
> > Marcin Giedz wrote:
> > > Dnia poniedzia??ek, 21 listopada 2005 11:23, Mario Splivalo napisa??:
> > > > Cool! Could you give specs on processors itself? The clock, cache,
> > > > and stuff?
> > >
> > > Look at this site once again - made some additional info.
> >
> > It says you have "2 x Opteron Dual Core" -- so is it two dual core CPUs,
> Exactly!!!

So the comparison is not really very fair. You are comparing the
performance of 4 Opterons versus 2 Xeons.

--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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TIP 6: explain analyze is your friend

On Mon, Nov 21, 2005 at 10:34:36AM +0100, Mario Splivalo wrote:
> > RAID5 generally doesn't make for a fast database. The problem is that
> > there is a huge amount of overhead everytime you go to write something
> > out to a RAID5 array. With careful tuning of the background writer you
> > might be able to avoid some of that penalty, though your read
> > performance will likely still be affected by the write overhead.
>
> RAID5 was not ment to improve performance, but to minimize disaster and
> downtime when your hard disk dies. We're using RAID5 with postgres. In
> the last 3 years we changed 5 disks, but the system downtime was zero
> minutes.

And the same would have been true with RAID10. In fact, RAID10 is more
reliable than RAID5; depending on what drives fail it's possible to lose
up to half of a RAID10 array without any data loss. If you ever lose
more than 2 drives at once with RAID5, your data is gone.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461

---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend

Way overkill... all you really need is a decently sized (160G or a pair of
80's) hard-disk and a P-III / AMD Athlon 750 MHz with 512MB Ram and FreeBSD
5 and postgreSQL....

With databases... it's all about disk-performance anyway...



""Michael D. Sofka"" <sofkam@rpi.edu> wrote in message
news:E8FEC853EDA289B924D8F213@betelgeuse.cct.rpi.e du...
> We are running PostgreSQL as the back-end to a spam scanning system. The
> database holds suspected spam, and user configuration information. A
> web interface allows people to accept, or (usually) discard the trapped
> messages. So, most data is write once, read at most once, delete.
>
> The total size of the db is about 16gig in size. And, we expect it
> could grow to 4 times this as more users are opted into spam scanning.
> During most of the day, the machine is only lightly loaded. There are
> two bursts of activity: the nightly vacuum, and the first thing in the
> morning spam checking.
>
> Our current db machine has two hyper-threaded 2.4 GHz Xeon processors, 4
> gig of main memory, and is attached to a JBOD configured with RAID 5 for
> the database, and mirrored disks for the DB logs.
>
> It is time to upgrade the machine. Two possibilities present themselves.
>
> 1. PowerEdge 6850
> 4 3.16 GHz Xeon processors
> 16 gig of memory
> Internal RAID 5 (only 3 disks)
> 2 Mirrored disks for root and db log.
>
> 2. PowerEdge 2850
> 2 Dual core 2.8GHz Xeon processors
> 8 gig of memory
> JBOD with RAID 5, and mirrored db log.
>
> Both configurations will cost about the same, within $\Delta$ for an
> acceptable value of $\Delta$. The idea behind the first is to keep the
> entire database in memory, by way of the disk cache. Alas, to keep it
> affordable (The extra memory is expensive) the JBOD must be jettisoned.
> The second is a larger version of our current configuration. (The 6850
> with a JBOD would stretch the budget beyond $\Delta$, and the expense
> would be difficult to justify.)
>
> I'm looking for any comments, or suggestions. With expected growth, the
> first configuration seems out of balance---it will likely start off
> fast, but with growth the slower disk configuration will likely be a
> problem. Is anybody running PostgreSQL in a large memory, slower disk
> configuration? What are your experiences.
>
> Thank You,
>
> Mike
>
> P.S. We are investigating if the current IBM JBOD will work with the
> Dell PERC cards. But, even if they do, the current JBOD is populated
> with soon to be extended warranty disks, and so progressively costly.
>
> --
> Michael D. Sofka sofkam@rpi.edu
> C&CT Sr. Systems Programmer Email, TeX, epistemology.
> Rensselaer Polytechnic Institute, Troy, NY. http://www.rpi.edu/~sofkam/
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>