Re: [PATCH] Lazy hashaggregate when no aggregation is needed

Ants Aasma <ants@cybertec.at> writes:
> A user complained on pgsql-performance that SELECT col FROM table
> GROUP BY col LIMIT 2; performs a full table scan. ISTM that it's safe
> to return tuples from hash-aggregate as they are found when no
> aggregate functions are in use. Attached is a first shot at that.

As I commented in the other thread, the user would be a lot better off
if he'd had an index on the column in question.  I'm not sure it's worth
complicating the hashagg logic when an indexscan + groupagg would
address the case better.
        regards, tom lane