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Re: postgres & smp

From: Thomas Graichen <news-list(dot)pgsql(dot)admin(at)innominate(dot)de>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: postgres & smp
Date: 2001-02-18 11:36:38
Message-ID: news2mail-96oc46$7tu$ (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
just to avoid confusion - some more things:

* smp and up case compared here were done on the same machine
  (linux 2.4.1-XFS, smp kernel booted with or without "nosmp")

* the used hardware is a 2 pII333 128mb ide disk

* the numbers were generated using pgbench from postgres-7.1beta4
  with -c 32 -s 20 -t 100

* the results are ranging from ~17tps (reiserfs/smp) ... ~20-23tps

one idea i have so far is that the pgbench queries are that simple
that the whole benchmark is heavily disk bound and the second cpu
only results in locking overhead resulting in a bit lower numbers)
may this be the reason for the missing improvement in the numbers
in the smp case?

again - a lot of thanks in advance


Thomas Graichen <news-list(dot)pgsql(dot)admin(at)innominate(dot)de> wrote:
> i hope this list is somewhat the right one for this ...

> i did some small tests with postgresql-71.beta4 on various
> filesystems (ext2, reiserfs, xfs) on two machines: 1 single
> cpu and one 2 cpu smp and was a bit surprised to see the tps
> results of the smp case to be lower than the one of the up case
> (also the running times of the used pgbench said the same)
> ... i was thinking that the load should spread over the cpu's
> and thus expected better results for smp - is there anything
> to take care of for smp with postgresql? did i anything
> wrong here?

> a lot of thanks in advance

> t

> p.s.: btw. i in all cases see about 15% better results with
>       the database running on an xfs filesystem compared to
>       ext2 ... reiserfs is about the same as ext2 but some-
>       times even worse ... just if anyone is interested ...

> -- 
> thomas(dot)graichen(at)innominate(dot)com
>                                                          innominate AG
>                                                   the linux architects
> tel: +49-30-308806-13   fax: -77   

                                                         innominate AG
                                                  the linux architects
tel: +49-30-308806-13   fax: -77   

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