Re: Group-count estimation statistics - Mailing list pgsql-hackers

From Stephen Frost
Subject Re: Group-count estimation statistics
Date
Msg-id 20050128182540.GA10437@ns.snowman.net
Whole thread Raw
In response to Group-count estimation statistics  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
* Tom Lane (tgl@sss.pgh.pa.us) wrote:
> The only real solution, of course, is to acquire cross-column
> statistics, but I don't see that happening in the near future.

That'd be nice, but sounds like alot of work.

> As a short-term hack, I am thinking that the "clamp to size of table"
> part of the rule is overly pessimistic, and that we should consider
> something like "clamp to size of table / 10" instead.  The justification
> for this is the thought that you aren't going to bother grouping unless
> it actually reduces the data volume.  We have used similar rules in the

I definitely agree with this.
Stephen

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