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Re: Abnormal performance difference between Postgres and MySQL

From: Farhan Husain <russoue(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Abnormal performance difference between Postgres and MySQL
Date: 2009-02-25 21:43:49
Message-ID: 3df32b6d0902251343g3a495103n2341bc625ce3b683@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
It was only after I got this high execution time when I started to look into
the configuration file and change those values. I tried several combinations
in which all those values were higher than the default values. I got no
improvement in runtime. The machine postgres is running on has 4 GB of RAM.

On Wed, Feb 25, 2009 at 3:40 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> >> > shared_buffers = 32MB                   # min 128kB or
> >> > max_connections*16kB
> >>
> >> That's REALLY small for pgsql.  Assuming your machine has at least 1G
> >> of ram, I'd set it to 128M to 256M as a minimum.
> >
> > As I wrote in a previous email, I had the value set to 1792MB (the
> highest I
> > could set) and had the same execution time. This value is not helping me
> to
> > bring down the execution time.
>
> No, you increased work_mem, not shared_buffers.  You might want to go
> and read the documentation:
>
>
> http://www.postgresql.org/docs/current/interactive/runtime-config-resource.html
>
> But at any rate, the large work_mem was producing a very strange plan.
>  It may help to see what the system does without that setting.  But
> changing shared_buffers will not change the plan, so let's not worry
> about that right now.
>
> ...Robert
>



-- 
Mohammad Farhan Husain
Research Assistant
Department of Computer Science
Erik Jonsson School of Engineering and Computer Science
University of Texas at Dallas

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