diff options
Diffstat (limited to 'doc/src/sgml')
| -rw-r--r-- | doc/src/sgml/catalogs.sgml | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml index 4baae556b31..196fdc6efdd 100644 --- a/doc/src/sgml/catalogs.sgml +++ b/doc/src/sgml/catalogs.sgml @@ -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"> @@ -3068,8 +3068,8 @@ </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, @@ -3077,13 +3077,22 @@ </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> |