Re: performance "tests" - Mailing list pgsql-admin

From Tom Lane
Subject Re: performance "tests"
Date
Msg-id 5607.1018453023@sss.pgh.pa.us
Whole thread Raw
In response to performance "tests"  (Raphael Bauduin <raphael@be.easynet.net>)
Responses Re: performance "tests"  (Naomi Walker <nwalker@eldocomp.com>)
Re: performance "tests"  (Bruce Momjian <pgman@candle.pha.pa.us>)
Re: performance "tests"  (Raphael Bauduin <raphael.bauduin@be.easynet.net>)
List pgsql-admin
Raphael Bauduin <raphael@be.easynet.net> writes:
> At some times, it seems to hang: it doesn't insert any rows for more
> than 10 seconds. At that time, the postmaster process takes 0%. Why is
> that?

At a guess, you're seeing the syncer daemon flushing a lot of dirty
kernel disk buffers out to disk, and thereby monopolizing disk I/O.
I haven't experimented too much with Linux, but on HPUX it's not
difficult for a sync() call to bring the system to its knees for many
seconds, if you've got application programs that have written a whole
lot of pages since the last sync.

> What's strange is that everything else hangs also! Would that be due
> to the CPU??

The CPU is free, but everything that wants to access disk is starved
for disk bandwidth ...

> ii  postgresql     7.1.3-7        Object-relational SQL database, descended fr

If you're going to run tests on foreign-key performance, please use
7.2.*.

            regards, tom lane

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