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.


Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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