| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Multivariate statistics and expression indexes |
| Date: | 2017-02-21 00:27:53 |
| Message-ID: | 01a586a9-fe88-ab56-0911-b09239acbc91@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On 02/21/2017 12:13 AM, Bruce Momjian wrote:
> At the risk of asking a stupid question, we already have optimizer
> statistics on expression indexes. In what sense are we using this for
> multi-variate statistics, and in what sense can't we.
>
We're not using that at all, because those are really orthogonal
features. Even with expression indexes, the statistics are per
attribute, and the attributes are treated as independent.
There was a proposal to also allow creating statistics on expressions
(without having to create an index), but that's not supported yet.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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