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First steps towards statistics on expressional (nee functional) indexes.

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This commit teaches ANALYZE to store such stats in pg_statistic, but
nothing is done yet about teaching the planner to use 'em.
Also, repair longstanding oversight in separate ANALYZE command: it
updated the pg_class.relpages and reltuples counts for the table proper,
but not for indexes.
This commit is contained in:
Tom Lane
2004-02-15 21:01:39 +00:00
parent 4b8f125973
commit f0c9397f80
7 changed files with 374 additions and 38 deletions
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21
doc/src/sgml/catalogs.sgml
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@ -1,6 +1,6 @@
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.83 2004/02/12 23:41:00 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.84 2004/02/15 21:01:38 tgl Exp $
-->
<chapter id="catalogs">
@ -3068,22 +3068,31 @@
</indexterm>
<para>
The catalog <structname>pg_statistic</structname> stores statistical data about
the contents of the database. Entries are created by
The catalog <structname>pg_statistic</structname> stores statistical data
about the contents of the database. Entries are created by
<command>ANALYZE</command> and subsequently used by the query planner.
There is one entry for each table column that has been analyzed.
Note that all the statistical data is inherently approximate,
even assuming that it is up-to-date.
</para>
<para>
<structname>pg_statistic</structname> also stores statistical data about
the values of index expressions. These are described as if they were
actual data columns; in particular, <structfield>starelid</structfield>
references the index. No entry is made for an ordinary non-expression
index column, however, since it would be redundant with the entry
for the underlying table column.
</para>
<para>
Since different kinds of statistics may be appropriate for different
kinds of data, <structname>pg_statistic</structname> is designed not
to assume very much about what sort of statistics it stores. Only
extremely general statistics (such as nullness) are given dedicated
columns in <structname>pg_statistic</structname>. Everything else
is stored in <quote>slots</quote>, which are groups of associated columns whose
content is identified by a code number in one of the slot's columns.
is stored in <quote>slots</quote>, which are groups of associated columns
whose content is identified by a code number in one of the slot's columns.
For more information see
<filename>src/include/catalog/pg_statistic.h</filename>.
</para>
@ -3117,7 +3126,7 @@
<entry><structfield>starelid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>The table that the described column belongs to</entry>
<entry>The table or index that the described column belongs to</entry>
</row>
<row>