Horton

Re: Group-count estimation statistics

Kris Jurka <books@ejurka.com>

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From: Kris Jurka <books@ejurka.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Greg Stark <gsstark@mit.edu>, pgsql-hackers@postgresql.org
Date: 2005-01-28T21:30:00Z
Lists: pgsql-hackers 

On Fri, 28 Jan 2005, Tom Lane wrote:

> you don't GROUP BY unique combinations of columns over huge
> tables --- or at least, you shouldn't expect great performance if you do.

The proposed change biases towards a hash plan which has no provision for
spilling to disk.  Slow is one thing, but excessive memory usage and
possibly failing is another thing.

Kris Jurka