Re: Poor performance on simple queries compared to sql server express - Mailing list pgsql-performance

Hello

It is little bit strange - can you send a info about your PostgreSQL version, send a query, and table description?

In this case, PostgreSQL should to use a hash aggregate, but from some strange reason, pg didn't do it.

Second strange issue is speed of external sort - it is less than I can expect.

What I know - a usual advice for MS Win is setting minimal shared bufferes - 512MB can be too much there.

Regards

Pavel Stehule

2013/8/26 Adam Ma'ruf <adam.maruf@gmail.com>

Hi,

I wasn't whether or not to mail to the novice mailing list of this one.  Since this is performance related I'm posting it here, but I am definitely a novice at postgresql - converting from mssql just now.

I have a ~2.5gb table with ~5M rows of data.  A query that groups by two fields and sums a floating field takes approximately 122 seconds.  The equivalent query takes ~ 8seconds in my previous sql server express installation.

I've tried to vary the parameters in postgresql.conf:

I've tried wavering shared buffers from 512mb to 4000mb

and working_mem from 64mb to 4000mb (i thought this might be the answer since the execution plan (referenced below) indicates that the sort relies on an External Merge Disk method)

I've increased the default_statistics_target  to 10000 and full vacuum analyzed

I realize there are no indexes on this table.  My main concern is why I can't get this to run as fast as in sql server express (which also has no indexes, and the same query takes about 8 seconds)

My system:  Windows Professional 64-bit

8 gb of ram

Intel i5-220M CPU @ 2.5GHz 

Here is the link to the execution plan:  http://explain.depesz.com/s/Ytx3

Thanks a lot in advance and do let me know if you require any more information to make an informed opinion,

A