Re: SQL performance issue with PostgreSQL compared to MySQL

Tom Lane wrote:
> Jeff Self <jself(at)nngov(dot)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.

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