2008/1/29, Vlad Marchenko <marchenko@gmail.com>:
> Tom:
>
> Yes, they are ints. To (somewhat) check your guess on the role of the hash
> aggregation speed, I just ran oltp test from sysbench
> (http://sysbench.sourceforge.net/docs/#database_mode) on a table with 1mln
> of records. That test uses pretty simple queries (that do not use
> aggregation) and 8.3 showed about the same performance as 8.2 (strictly
> speaking 8.3 was about 1-2% slower, but not 10-15% like on my query).
>
> I'm curious if that new hash aggregation algorithm was put in 8.3 with the
> performance increase as a goal or it was simply a required change to support
> some other new feature of 8.3? Right now the switch from 8.2 to 8.3 doesn't
> seems a favorable step for the type of application that we have...
Vlad,
What happens if you run the 8.3 test with enable_hashagg set to off?
Saudações, Clodoaldo Pinto Neto
> ----- Original Message -----
> From: "Tom Lane" <tgl@sss.pgh.pa.us>
> To: "Vlad" <marchenko@gmail.com>
> Cc: "PG-General" <pgsql-general@postgresql.org>
> Sent: Monday, January 28, 2008 9:13 PM
> Subject: Re: [GENERAL] 8.3RC2 vs 8.2.6 testing results
>
>
> > Vlad <marchenko@gmail.com> writes:
> >> 2. We ran several tests and found 8.3 generally 10% slower than 8.2.6.
> >
> > The particular case you are showing here seems to be all about the speed
> > of hash aggregation --- at least the time differential is mostly in the
> > HashAggregate step. What is the data type of a_id? I speculate that
> > you're noticing the slightly slower/more complicated hash function that
> > 8.3 uses for integers. On a case where the data was well distributed
> > you'd not see any countervailing efficiency gain from those extra
> > cycles.
> >
> > regards, tom lane
> >
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
>