catalogs.sgml

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

     </row>

     <row>
      <entry><structfield>anl_scale_factor</structfield></entry>
      <entry><type>float4</type></entry>
      <entry></entry>
      <entry>Multiplier for reltuples to add to
       <structfield>anl_base_thresh</></entry>
     </row>

     <row>
      <entry><structfield>vac_cost_delay</structfield></entry>
      <entry><type>integer</type></entry>
      <entry></entry>
      <entry>Custom <varname>vacuum_cost_delay</> parameter</entry>
     </row>

     <row>
      <entry><structfield>vac_cost_limit</structfield></entry>
      <entry><type>integer</type></entry>
      <entry></entry>
      <entry>Custom <varname>vacuum_cost_limit</> parameter</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The autovacuum daemon will initiate a <command>VACUUM</> operation
   on a particular table when the number of updated or deleted tuples
   exceeds <structfield>vac_base_thresh</structfield> plus
   <structfield>vac_scale_factor</structfield> times the number of
   live tuples currently estimated to be in the relation.
   Similarly, it will initiate an <command>ANALYZE</> operation
   when the number of inserted, updated or deleted tuples
   exceeds <structfield>anl_base_thresh</structfield> plus
   <structfield>anl_scale_factor</structfield> times the number of
   live tuples currently estimated to be in the relation.
  </para>

  <para>
   Any of the numerical fields can contain <literal>-1</> (or indeed
   any negative value) to indicate that the system-wide default should
   be used for this particular value.  Observe that the
   <structfield>vac_cost_delay</> variable inherits its default value from the
   <varname>autovacuum_vacuum_cost_delay</> configuration parameter,
   or from <varname>vacuum_cost_delay</> if the former is set to a negative
   value.  The same applies to <structfield>vac_cost_limit</>.
  </para>

 </sect1>


 <sect1 id="catalog-pg-cast">
  <title><structname>pg_cast</structname></title>

  <indexterm zone="catalog-pg-cast">
   <primary>pg_cast</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_cast</structname> stores data type conversion paths,
   both built-in paths and those defined with <command>CREATE CAST</command>.
  </para>

  <table>
   <title><structfield>pg_cast</> 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>castsource</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
      <entry>OID of the source data type</entry>
     </row>

     <row>
      <entry><structfield>casttarget</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
      <entry>OID of the target data type</entry>
     </row>

     <row>
      <entry><structfield>castfunc</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
      <entry>
       The OID of the function to use to perform this cast.  Zero is
       stored if the data types are binary compatible (that is, no
       run-time operation is needed to perform the cast).
      </entry>
     </row>

     <row>
      <entry><structfield>castcontext</structfield></entry>
      <entry><type>char</type></entry>
      <entry></entry>
      <entry>
       Indicates what contexts the cast may be invoked in.
       <literal>e</> means only as an explicit cast (using
       <literal>CAST</> or <literal>::</> syntax).
       <literal>a</> means implicitly in assignment
       to a target column, as well as explicitly.
       <literal>i</> means implicitly in expressions, as well as the
       other cases.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The cast functions listed in <structname>pg_cast</structname> must
   always take the cast source type as their first argument type, and
   return the cast destination type as their result type.  A cast
   function can have up to three arguments.  The second argument,
   if present, must be type <type>integer</>; it receives the type
   modifier associated with the destination type, or <literal>-1</>
   if there is none.  The third argument,
   if present, must be type <type>boolean</>; it receives <literal>true</>
   if the cast is an explicit cast, <literal>false</> otherwise.
  </para>

  <para>
   It is legitimate to create a <structname>pg_cast</structname> entry
   in which the source and target types are the same, if the associated
   function takes more than one argument.  Such entries represent
   <quote>length coercion functions</> that coerce values of the type
   to be legal for a particular type modifier value.  Note however that
   at present there is no support for associating non-default type
   modifiers with user-created data types, and so this facility is only
   of use for the small number of built-in types that have type modifier
   syntax built into the grammar.
  </para>

  <para>
   When a <structname>pg_cast</structname> entry has different source and
   target types and a function that takes more than one argument, it
   represents converting from one type to another and applying a length
   coercion in a single step.  When no such entry is available, coercion
   to a type that uses a type modifier involves two steps, one to
   convert between data types and a second to apply the modifier.
  </para>
 </sect1>

 <sect1 id="catalog-pg-class">
  <title><structname>pg_class</structname></title>

  <indexterm zone="catalog-pg-class">
   <primary>pg_class</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_class</structname> catalogs tables and most
   everything else that has columns or is otherwise similar to a
   table.  This includes indexes (but see also
   <structname>pg_index</structname>), sequences, views, composite types,
   and some kinds of special relation; see <structfield>relkind</>.
   Below, when we mean all of these
   kinds of objects we speak of <quote>relations</quote>.  Not all
   columns are meaningful for all relation types.
  </para>

  <table>
   <title><structname>pg_class</> 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>relname</structfield></entry>
      <entry><type>name</type></entry>
      <entry></entry>
      <entry>Name of the table, index, view, etc.</entry>
     </row>

     <row>
      <entry><structfield>relnamespace</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
      <entry>
       The OID of the namespace that contains this relation
      </entry>
     </row>

     <row>
      <entry><structfield>reltype</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
      <entry>
       The OID of the data type that corresponds to this table's row type,
       if any (zero for indexes, which have no <structname>pg_type</> entry)
      </entry>
     </row>

     <row>
      <entry><structfield>relowner</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
      <entry>Owner of the relation</entry>
     </row>

     <row>
      <entry><structfield>relam</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
      <entry>If this is an index, the access method used (B-tree, hash, etc.)</entry>
     </row>

     <row>
      <entry><structfield>relfilenode</structfield></entry>
      <entry><type>oid</type></entry>
      <entry></entry>
      <entry>Name of the on-disk file of this relation; 0 if none</entry>
     </row>

     <row>
      <entry><structfield>reltablespace</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
      <entry>
       The tablespace in which this relation is stored.  If zero,
       the database's default tablespace is implied.  (Not meaningful
       if the relation has no on-disk file.)
      </entry>
     </row>

     <row>
      <entry><structfield>relpages</structfield></entry>
      <entry><type>int4</type></entry>
      <entry></entry>
      <entry>
       Size of the on-disk representation of this table in pages (of size
       <symbol>BLCKSZ</symbol>).
       This is only an estimate used by the planner.
       It is updated by <command>VACUUM</command>,
       <command>ANALYZE</command>, and a few DDL commands
       such as <command>CREATE INDEX</command>.
      </entry>
     </row>

     <row>
      <entry><structfield>reltuples</structfield></entry>
      <entry><type>float4</type></entry>
      <entry></entry>
      <entry>
       Number of rows in the table.
       This is only an estimate used by the planner.
       It is updated by <command>VACUUM</command>,
       <command>ANALYZE</command>, and a few DDL commands
       such as <command>CREATE INDEX</command>.
      </entry>
     </row>

     <row>
      <entry><structfield>reltoastrelid</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
      <entry>
       OID of the TOAST table associated with this table, 0 if none.
       The TOAST table stores large attributes <quote>out of
       line</quote> in a secondary table.
      </entry>
     </row>

     <row>
      <entry><structfield>reltoastidxid</structfield></entry>
      <entry><type>oid</type></entry>
      <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
      <entry>
       For a TOAST table, the OID of its index.  0 if not a TOAST table.
      </entry>
     </row>

     <row>
      <entry><structfield>relhasindex</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>
       True if this is a table and it has (or recently had) any
       indexes. This is set by <command>CREATE INDEX</command>, but
       not cleared immediately by <command>DROP INDEX</command>.
       <command>VACUUM</command> clears <structfield>relhasindex</> if it finds the
       table has no indexes.
      </entry>
     </row>

     <row>
      <entry><structfield>relisshared</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>True if this table is shared across all databases in the
      cluster.  Only certain system catalogs (such as
      <structname>pg_database</structname>) are shared.</entry>
     </row>

     <row>
      <entry><structfield>relkind</structfield></entry>
      <entry><type>char</type></entry>
      <entry></entry>
      <entry>
       <literal>r</> = ordinary table, <literal>i</> = index,
       <literal>S</> = sequence, <literal>v</> = view, <literal>c</> =
       composite type, <literal>s</> = special, <literal>t</> = TOAST
       table
      </entry>
     </row>

     <row>
      <entry><structfield>relnatts</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>
       Number of user columns in the relation (system columns not
       counted).  There must be this many corresponding entries in
       <structname>pg_attribute</structname>.  See also
       <literal>pg_attribute.attnum</literal>.
      </entry>
     </row>

     <row>
      <entry><structfield>relchecks</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>
       Number of check constraints on the table; see
       <structname>pg_constraint</structname> catalog
      </entry>
     </row>

     <row>
      <entry><structfield>reltriggers</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>
       Number of triggers on the table; see
       <structname>pg_trigger</structname> catalog
      </entry>
     </row>

     <row>
      <entry><structfield>relukeys</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>unused  (<emphasis>not</emphasis> the number of unique keys)</entry>
     </row>

     <row>
      <entry><structfield>relfkeys</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>unused  (<emphasis>not</emphasis> the number of foreign keys on the table)</entry>
     </row>

     <row>
      <entry><structfield>relrefs</structfield></entry>
      <entry><type>int2</type></entry>
      <entry></entry>
      <entry>unused</entry>
     </row>

     <row>
      <entry><structfield>relhasoids</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>
       True if we generate an OID for each row of the relation.
      </entry>
     </row>

     <row>
      <entry><structfield>relhaspkey</structfield></entry>
      <entry><type>bool</type></entry>
      <entry></entry>
      <entry>
       True if the table has (or once had) a primary key.
      </entry>
     </row>

     <row>
      <entry><structfield>relhasrules</structfield></entry>