catalogs.sgml

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

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 Documentation of the system catalogs, directed toward PostgreSQL developers
 $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.115 2005/11/04 23:13:59 petere Exp $
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<chapter id="catalogs">
 <title>System Catalogs</title>

  <para>
   The system catalogs are the place where a relational database
   management system stores schema metadata, such as information about
   tables and columns, and internal bookkeeping information.
   <productname>PostgreSQL</productname>'s system catalogs are regular
   tables.  You can drop and recreate the tables, add columns, insert
   and update values, and severely mess up your system that way.
   Normally, one should not change the system catalogs by hand, there
   are always SQL commands to do that.  (For example, <command>CREATE
   DATABASE</command> inserts a row into the
   <structname>pg_database</structname> catalog &mdash; and actually
   creates the database on disk.)  There are some exceptions for
   particularly esoteric operations, such as adding index access methods.
  </para>

 <sect1 id="catalogs-overview">
  <title>Overview</title>

  <para>
   <xref linkend="catalog-table"> lists the system catalogs.
   More detailed documentation of each catalog follows below.
  </para>

  <para>
   Most system catalogs are copied from the template database during
   database creation and are thereafter database-specific. A few
   catalogs are physically shared across all databases in a cluster;
   these are noted in the descriptions of the individual catalogs.
  </para>

  <table id="catalog-table">
   <title>System Catalogs</title>

   <tgroup cols="2">
    <thead>
     <row>
      <entry>Catalog Name</entry>
      <entry>Purpose</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><link linkend="catalog-pg-aggregate"><structname>pg_aggregate</structname></link></entry>
      <entry>aggregate functions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>
      <entry>index access methods</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-amop"><structname>pg_amop</structname></link></entry>
      <entry>access method operators</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link></entry>
      <entry>access method support procedures</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link></entry>
      <entry>column default values</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link></entry>
      <entry>table columns (<quote>attributes</quote>)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link></entry>
      <entry>authorization identifiers (roles)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link></entry>
      <entry>authorization identifier membership relationships</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-autovacuum"><structname>pg_autovacuum</structname></link></entry>
      <entry>per-relation autovacuum configuration parameters</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-cast"><structname>pg_cast</structname></link></entry>
      <entry>casts (data type conversions)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-class"><structname>pg_class</structname></link></entry>
      <entry>tables, indexes, sequences, views (<quote>relations</quote>)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link></entry>
      <entry>check constraints, unique constraints, primary key constraints, foreign key constraints</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-conversion"><structname>pg_conversion</structname></link></entry>
      <entry>encoding conversion information</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-database"><structname>pg_database</structname></link></entry>
      <entry>databases within this database cluster</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-depend"><structname>pg_depend</structname></link></entry>
      <entry>dependencies between database objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-description"><structname>pg_description</structname></link></entry>
      <entry>descriptions or comments on database objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-index"><structname>pg_index</structname></link></entry>
      <entry>additional index information</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-inherits"><structname>pg_inherits</structname></link></entry>
      <entry>table inheritance hierarchy</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-language"><structname>pg_language</structname></link></entry>
      <entry>languages for writing functions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-largeobject"><structname>pg_largeobject</structname></link></entry>
      <entry>large objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-listener"><structname>pg_listener</structname></link></entry>
      <entry>asynchronous notification support</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link></entry>
      <entry>schemas</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link></entry>
      <entry>index access method operator classes</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link></entry>
      <entry>operators</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-pltemplate"><structname>pg_pltemplate</structname></link></entry>
      <entry>template data for procedural languages</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link></entry>
      <entry>functions and procedures</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link></entry>
      <entry>query rewrite rules</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link></entry>
      <entry>dependencies on shared objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link></entry>
      <entry>planner statistics</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link></entry>
      <entry>tablespaces within this database cluster</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link></entry>
      <entry>triggers</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-type"><structname>pg_type</structname></link></entry>
      <entry>data types</entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-aggregate">
  <title><structname>pg_aggregate</structname></title>

  <indexterm zone="catalog-pg-aggregate">
   <primary>pg_aggregate</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_aggregate</structname> stores information about
   aggregate functions.  An aggregate function is a function that
   operates on a set of values (typically one column from each row
   that matches a query condition) and returns a single value computed
   from all these values.  Typical aggregate functions are
   <function>sum</function>, <function>count</function>, and
   <function>max</function>.  Each entry in
   <structname>pg_aggregate</structname> is an extension of an entry
   in <structname>pg_proc</structname>.  The <structname>pg_proc</structname>
   entry carries the aggregate's name, input and output data types, and
   other information that is similar to ordinary functions.
  </para>

  <table>
   <title><structname>pg_aggregate</> Columns</title>

   <tgroup cols=4>
    <thead>
     <row>
      <entry>Name</entry>
      <entry>Type</entry>
      <entry>References</entry>
      <entry>Description</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry><structfield>aggfnoid</structfield></entry>
      <entry><type>regproc</type></entry>
      <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
      <entry><structname>pg_proc</structname> OID of the aggregate function</entry>
     </row>
     <row>
      <entry><structfield>aggtransfn</structfield></entry>
      <entry><type>regproc</type></entry>
      <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
      <entry>Transition function</entry>
     </row>
     <row>
      <entry><structfield>aggfinalfn</structfield></entry>
      <entry><type>regproc</type></entry>
      <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
      <entry>Final function (zero if none)</entry>
     </row>
     <row>
      <entry><structfield>aggsortop</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
      <entry>Associated sort operator (zero if none)</entry>
     </row>
     <row>
      <entry><structfield>aggtranstype</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
      <entry>Data type of the aggregate function's internal transition (state) data</entry>
     </row>
     <row>
      <entry><structfield>agginitval</structfield></entry>
      <entry><type>text</type></entry>
      <entry></entry>
      <entry>
       The initial value of the transition state.  This is a text
       field containing the initial value in its external string
       representation.  If this field is null, the transition state
       value starts out null.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   New aggregate functions are registered with the <command>CREATE
   AGGREGATE</command> command.  See <xref linkend="xaggr"> for more
   information about writing aggregate functions and the meaning of
   the transition functions, etc.
  </para>

 </sect1>


 <sect1 id="catalog-pg-am">
  <title><structname>pg_am</structname></title>

  <indexterm zone="catalog-pg-am">
   <primary>pg_am</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_am</structname> stores information about index
   access methods.  There is one row for each index access method supported by
   the system.  The contents of this catalog are discussed in detail in
   <xref linkend="indexam">.
  </para>

  <table>
   <title><structname>pg_am</> Columns</title>

   <tgroup cols=4>
    <thead>
     <row>
      <entry>Name</entry>
      <entry>Type</entry>
      <entry>References</entry>
      <entry>Description</entry>
     </row>
    </thead>
    <tbody>

     <row>
      <entry><structfield>amname</structfield></entry>
      <entry><type>name</type></entry>
      <entry></entry>
      <entry>Name of the access method</entry>
     </row>

     <row>
      <entry><structfield>amstrategies</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>Number of operator strategies for this access method</entry>
     </row>

     <row>
      <entry><structfield>amsupport</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>Number of support routines for this access method</entry>
     </row>

     <row>
      <entry><structfield>amorderstrategy</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>Zero if the index offers no sort order, otherwise the strategy
      number of the strategy operator that describes the sort order</entry>
     </row>

     <row>
      <entry><structfield>amcanunique</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>Does the access method support unique indexes?</entry>
     </row>

     <row>
      <entry><structfield>amcanmulticol</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>Does the access method support multicolumn indexes?</entry>
     </row>

     <row>
      <entry><structfield>amoptionalkey</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>Does the access method support a scan without any constraint
       for the first index column?</entry>
     </row>

     <row>
      <entry><structfield>amindexnulls</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>Does the access method support null index entries?</entry>
     </row>

     <row>
      <entry><structfield>amconcurrent</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>Does the access method support concurrent updates?</entry>
     </row>

     <row>
      <entry><structfield>aminsert</structfield></entry>
      <entry><type>regproc</type></entry>