Re: Tuning for mid-size server

Josh,

The 6650 can have upto 32GB of RAM.

There are 5 drives. In future, they will be replaced by a fiber array -
hopefully.

I read an article that suggests you 'start' with 25% of memory for
shared_buffers. Sort memory was suggested to be at 2-4%. Here's the
link:
http://www.ca.postgresql.org/docs/momjian/hw_performance/node8.html
Maybe, I misinterpreted it.

I read the document on
http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html and the
suggested values are much lower than what I have mentioned here. It
won't hurt to start with lower numbers and increase lateron if needed.

Thanks,
Anjan

-----Original Message-----
From: Josh Berkus [mailto:josh(at)agliodbs(dot)com]
Sent: Tuesday, October 21, 2003 12:21 PM
To: Anjan Dave; pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] Tuning for mid-size server

Anjan,

> Pretty soon, a PowerEdge 6650 with 4 x 2Ghz XEONs, and 8GB Memory,
> with internal drives on RAID5 will be delivered. Postgres will be from

> RH8.0.

How many drives? RAID5 sucks for heavy read-write databases, unless
you have
5+ drives. Or a large battery-backed cache.

Also, last I checked, you can't address 8GB of RAM without a 64-bit
processor.
Since when are the Xeons 64-bit?

> Shared_buffers (25% of RAM / 8KB)) = 8589934592 * .25 / 8192 = 262144

That's too high. Cut it in half at least. Probably down to 5% of
available
RAM.

> Sort_mem (4% of RAM / 1KB) = 335544. We'll take about half of that -
> 167772

Fine if you're running a few-user-large-operation database. If this is
a
webserver, you want a much, much lower value.

> Effective_cache_size = 262144 (same as shared_buffers - 25%)

Much too low. Where did you get these calculations, anyway?

> In a generic sense, these are recommended values I found in some
> documents.

Where? We need to contact the author of the "documents" and tell them
to
correct things.

> joins, orderby, groupby clauses. The web application is based on
> Apache/Resin and hotspot JVM 1.4.0.

You'll need to estimate the memory consumed by Java & Apache to have
realistic
figures to work with.

> Are the above settings ok to begin with? Are there any other
> parameters that I should configure now, or monitor lateron?

No, they're not. See:
http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html to tune
these
parameters.

--
Josh Berkus
Aglio Database Solutions
San Francisco