Re: Abnormal performance difference between Postgres and MySQL

[Farhan Husain <russoue@xxxxxxxxx>]

I am trying to find the reason of the problem so going to Oracle or something else is not the solution. I tried with several combinations of those parameters before posting the problem here. I have read http://www.postgresql.org/docs/current/interactive/runtime-config-resource.html before and I think I understood what it said.

2009/2/25 Akos Gabriel <akos.gabriel@xxxxxxxxxx>

Wed, 25 Feb 2009 15:43:49 -0600 -n
Farhan Husain <russoue@xxxxxxxxx> írta:

OK, you have two options:

1. Learn to read carefully, and differentiate between work_mem and
shared_buffers options. Lower work_mem and rise shared_buffers as
others wrote.
2. Leave Postgresql alone and go for Oracle or Microsoft SQL...

Rgds,
Akos

> 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@xxxxxxxxx>
> 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
> >
>
>
>


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