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Add the ability to store inheritance-tree statistics in pg_statistic,

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and teach ANALYZE to compute such stats for tables that have subclasses.
Per my proposal of yesterday.

autovacuum still needs to be taught about running ANALYZE on parent tables
when their subclasses change, but the feature is useful even without that.
This commit is contained in:
Tom Lane
2009-12-29 20:11:45 +00:00
parent 84d723b6ce
commit 649b5ec7c8
18 changed files with 407 additions and 177 deletions
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37
doc/src/sgml/catalogs.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.214 2009/12/17 14:36:15 rhaas Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.215 2009/12/29 20:11:42 tgl Exp $ -->
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
-->
@ -4506,19 +4506,32 @@
The catalog <structname>pg_statistic</structname> stores
statistical data about the contents of the database. Entries are
created by <xref linkend="sql-analyze" endterm="sql-analyze-title">
and subsequently used by the query planner. There is one entry for
each table column that has been analyzed. Note that all the
and subsequently used by the query planner. Note that all the
statistical data is inherently approximate, even assuming that it
is up-to-date.
</para>
<para>
Normally there is one entry, with <structfield>stainherit</> =
<literal>false</>, for each table column that has been analyzed.
If the table has inheritance children, a second entry with
<structfield>stainherit</> = <literal>true</> is also created. This row
represents the column's statistics over the inheritance tree, i.e.,
statistics for the data you'd see with
<literal>SELECT <replaceable>column</> FROM <replaceable>table</>*</literal>,
whereas the <structfield>stainherit</> = <literal>false</> row represents
the results of
<literal>SELECT <replaceable>column</> FROM ONLY <replaceable>table</></literal>.
</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.
for the underlying table column. Currently, entries for index expressions
always have <structfield>stainherit</> = <literal>false</>.
</para>
<para>
@ -4572,6 +4585,14 @@
<entry>The number of the described column</entry>
</row>
<row>
<entry><structfield>stainherit</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If true, the stats include inheritance child columns, not just the
values in the specified relation</entry>
</row>
<row>
<entry><structfield>stanullfrac</structfield></entry>
<entry><type>float4</type></entry>
@ -7114,6 +7135,14 @@
<entry>Name of the column described by this row</entry>
</row>
<row>
<entry><structfield>inherited</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>If true, this row includes inheritance child columns, not just the
values in the specified table</entry>
</row>
<row>
<entry><structfield>null_frac</structfield></entry>
<entry><type>real</type></entry>