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Re: Abnormal performance difference between Postgres and MySQL

From: Farhan Husain <russoue(at)gmail(dot)com>
To: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Abnormal performance difference between Postgres and MySQL
Date: 2009-02-25 21:56:58
Message-ID: 3df32b6d0902251356p28339bc6tac00404fcbd4177a@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, Feb 25, 2009 at 3:55 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>wrote:

> On Wed, Feb 25, 2009 at 2:38 PM, Farhan Husain <russoue(at)gmail(dot)com> wrote:
> >
> >
> > On Wed, Feb 25, 2009 at 3:35 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
> > wrote:
> >>
> >> On Wed, Feb 25, 2009 at 2:32 PM, Farhan Husain <russoue(at)gmail(dot)com>
> wrote:
> >> >
> >> > On Wed, Feb 25, 2009 at 3:30 PM, Robert Haas <robertmhaas(at)gmail(dot)com>
> >> > wrote:
> >> >>
> >> >> On Wed, Feb 25, 2009 at 3:44 PM, Farhan Husain <russoue(at)gmail(dot)com>
> >> >> wrote:
> >> >> > Initially, it was the default value (32MB). Later I played with
> that
> >> >> > value
> >> >> > thinking that it might improve the performance. But all the values
> >> >> > resulted
> >> >> > in same amount of time.
> >> >>
> >> >> Well, if you set it back to what we consider to be a reasonable
> value,
> >> >> rerun EXPLAIN ANALYZE, and post that plan, it might help us tell you
> >> >> what to do next.
> >> >>
> >> >> ...Robert
> >> >
> >> > Right now I am running the query again with 32MB work_mem. It is
> taking
> >> > a
> >> > long time as before. However, I have kept the following values
> >> > unchanged:
> >> >
> >> > 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, that was work_mem.  This is shared_buffers.
>

Oh, sorry for the confusion. I will change the shared_buffer once the
current run finishes.

-- 
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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