| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | PostgreSQL - Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, PostgreSQL-development Hackers <pgsql-hackers(at)postgresql(dot)org>, Boszormenyi Zoltan <zb(at)cybertec(dot)at> |
| Subject: | Re: cross column correlation revisted |
| Date: | 2010-07-14 15:13:06 |
| Message-ID: | AANLkTilhOhWYI_yBWYXY0OWIi1xcd6q-XwJNTuHhm9_t@mail.gmail.com |
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| Lists: | pgsql-hackers |
2010/7/14 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> If the combination of columns is actually interesting, there might well
> be an index in place, or the DBA might be willing to create it.
Indexes aren't free, though, nor even close to it.
Still, I think we should figure out the underlying mechanism first and
then design the interface afterwards. One idea I had was a way to say
"compute the MCVs and histogram buckets for this table WHERE
<predicate>". If you can prove predicate for a particular query, you
can use the more refined statistics in place of the full-table
statistics. This is fine for the breast cancer case, but not so
useful for the zip code/street name case (which seems to be the really
tough one).
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company
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