Re: Abnormal performance difference between Postgres and MySQL

[Farhan Husain <russoue@xxxxxxxxx>]

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

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