Re: Problem with grouping, uses Sort and GroupAggregate, HashAggregate is better(?)

[Rolf Østvik (HA/EXA) <rolf(dot)ostvik(at)ericsson(dot)com>]

> -----Original Message-----
> From: Dave Dutcher [mailto:dave(at)tridecap(dot)com] 
> Sent: Sunday, January 14, 2007 5:12 PM
> To: Rolf Østvik (HA/EXA); pgsql-performance(at)postgresql(dot)org
> Subject: RE: [PERFORM] Problem with grouping, uses Sort and 
> GroupAggregate, HashAggregate is better(?)
> 
> > -----Original Message-----
> > From: pgsql-performance-owner(at)postgresql(dot)org 
> > [mailto:pgsql-performance-owner(at)postgresql(dot)org] On Behalf Of 
> > Rolf Østvik (HA/EXA)
> 
> Have you tried "set enable_sort=off" with 8.1.2?  I'm not 
> sure if that will
> change anything because it has to do at least one sort.  Its 
> just a lots
> faster to do a hashagg + small sort than one big sort in this 
> case.  (I
> wonder if there should be enable_groupagg?)    

Did you mean enable_sort = 'off' for 8.2.1?


I tried to set enable_sort = 'off' for both the
8.1.4 server and the 8.2.1 server.
Both servers used the same plan as Run 4 and Run 3 respectively.
There were of course some changes in the planner cost for the sort 
steps, but the execution times was of course the same.

Regards
Rolf Østvik