From: | Stephen Frost <sfrost(at)snowman(dot)net> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Group-count estimation statistics |
Date: | 2005-01-28 18:25:40 |
Message-ID: | 20050128182540.GA10437@ns.snowman.net |
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Lists: | pgsql-hackers |
* Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)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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