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Re: postgresql meltdown on PlanetMath.org

From: Florian Weimer <Weimer(at)CERT(dot)Uni-Stuttgart(dot)DE>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: postgresql meltdown on PlanetMath.org
Date: 2003-03-20 23:01:18
Message-ID: 87fzphk5hd.fsf@Login.CERT.Uni-Stuttgart.DE (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> You definitely need to increase the fsm shared memory parameters.  The
> default max_fsm_relations is just plain too small (try 1000) and the
> default_max_fsm_pages is really only enough for perhaps a 100Mb
> database.  I'd try bumping it to 100,000.  Note you need a postmaster
> restart to make these changes take effect.

Hmm, are there any guidelines for choosing these values?

We have a database with a table into which we insert about 4,000,000
rows each day, and delete another 4,000,000 rows.  The total row count
is around 40 million, I guess, and the rows are about 150 bytes long.
(VACUUM FULL is running at the moment, so I can't check.)

The database is used as a research tool, and we run moderately complex
ad-hoc queries on it.  As a consequence, I don't see much room for
optimization.

One of the columns is time-based and indexed, so we suffer from the
creeping index syndrome.  A nightly index rebuild followed by a VACUUM
ANALYZE isn't a problem (it takes less than six ours), but this
doesn't seem to be enough (we seem to lose disk space nevertheless).

I can't afford a regular VACUUM FULL because it takes down the
database for over ten hours, and this starts to cut into the working
hours no matter when it starts.

Can you suggest some tweaks to the FSM values so that we can avoid the
full VACUUM?  The database runs 7.3.2 and resides on a 4-way Xeon box
with 4 GB of RAM and a severely underpowered disk subsystem (Linux
software RAID1 on two 10k 36 GB SCSI drives -- don't ask, this
database application is nothing but an accident which happened after
purchase of the box).

-- 
Florian Weimer 	                  Weimer(at)CERT(dot)Uni-Stuttgart(dot)DE
University of Stuttgart           http://CERT.Uni-Stuttgart.DE/people/fw/
RUS-CERT                          fax +49-711-685-5898

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