Re: SQL performance issue with PostgreSQL compared to MySQL

Tom Lane wrote:
> Jeff Self <jself@nngov.com> writes:
> > if it's too OT, let me know, and I'll stop. The query "SELECT authuser,
> > SUM(bytes) AS traffic FROM logfile GROUP BY authuser ORDER BY traffic"
> > [is slow]
> 
> What datatype are the columns used in the query?  And what PG version
> are we talking about?

My guess is that is the lack of hashing for GROUP BY aggregating that is
killing us.  TODO has:
* Add hash for evaluating GROUP BY aggregates

and I specifically remember MySQL has such a hash. The big question is
how many unique values are there in the group.  If it is large, the
missing hashing could be the problem.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026