From: | Ray Ontko <rayo(at)ontko(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Ray Ontko <rayo(at)ontko(dot)com>, pgsql-admin(at)postgresql(dot)org |
Subject: | Re: Are statistics gathered on function indexes? |
Date: | 2002-06-28 20:42:01 |
Message-ID: | 200206282042.PAA07634@shire.ontko.com |
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Lists: | pgsql-admin |
Tom,
> Ray Ontko <rayo(at)ontko(dot)com> writes:
> > 1) here's the "bad" stats.
> > 2) here's the "good" stats.
> > Note that the information really is different.
>
> Yeah. It seems that the critical difference is the null_frac; if I take
> your "bad" values and change null_frac to 0 then I get
> reasonable-looking answers, but with null_frac = 0.000333333 I indeed
> get bad answers. I suspect null_frac is getting double-counted
> somewhere, and depending on just how many nulls ANALYZE happens to find,
> you might get pushed over the edge from a small selectivity to zero or
> negative selectivity. Will dig further.
Does this help?
develop=# select count(*) from actor where actor_full_name is not null ;
count
--------
433809
(1 row)
develop=# select count(*) from actor ;
count
--------
433902
(1 row)
Ray
----------------------------------------------------------------------
Ray Ontko rayo(at)ontko(dot)com Phone 1.765.935.4283 Fax 1.765.962.9788
Ray Ontko & Co. Software Consulting Services http://www.ontko.com/
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