Bruce Momjian wrote:
> Alvaro Herrera wrote:
> > Karl Denninger escribi?:
> >
> > > The individual boolean fields don't kill me and in terms of some of the
> > > application issues they're actually rather easy to code for.
> > >
> > > The problem with re-coding for them is extensibility (by those who
> > > install and administer the package); a mask leaves open lots of extra
> > > bits for "site-specific" use, where hard-coding booleans does not, and
> > > since the executable is a binary it instantly becomes a huge problem for
> > > everyone but me.
> >
> > Did you try hiding the bitmask operations inside a function as Tom
> > suggested?
>
> Yes. In addition, functions that are part of expression indexes do get
> their own optimizer statistics, so it does allow you to get optimizer
> stats for your test without having to use booleans.
>
> I see this documented in the 8.0 release notes:
>
> * "ANALYZE" now collects statistics for expression indexes (Tom)
> Expression indexes (also called functional indexes) allow users
> to index not just columns but the results of expressions and
> function calls. With this release, the optimizer can gather and
> use statistics about the contents of expression indexes. This will
> greatly improve the quality of planning for queries in which an
> expression index is relevant.
>
> Is this in our main documentation somewhere?
Added with attached, applied patch.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
PG East: http://www.enterprisedb.com/community/nav-pg-east-2010.do
+ If your life is a hard drive, Christ can be your backup. +
Index: doc/src/sgml/maintenance.sgml
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SET STATISTICS</>, or change the database-wide default using the <xref
linkend="guc-default-statistics-target"> configuration parameter.
</para>
+
+ <para>
+ Also, by default there is limited information available about
+ the selectivity of functions. However, if you create an expression
+ index that uses a function call, useful statistics will be
+ gathered about the function, which can greatly improve query
+ plans that use the expression index.
+ </para>
</tip>
</sect2>
