Sophie: postgresql8.3-docs-8.3.6-2mdv2008.1 x86

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><A
NAME="MANAGE-AG-TABLESPACES"
>20.6. Tablespaces</A
></H1
><A
NAME="AEN26219"
></A
><P
>   Tablespaces in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allow database administrators to
   define locations in the file system where the files representing
   database objects can be stored. Once created, a tablespace can be referred
   to by name when creating database objects.
  </P
><P
>   By using tablespaces, an administrator can control the disk layout
   of a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation. This is useful in at
   least two ways. First, if the partition or volume on which the
   cluster was initialized runs out of space and cannot be extended,
   a tablespace can be created on a different partition and used
   until the system can be reconfigured.
  </P
><P
>   Second, tablespaces allow an administrator to use knowledge of the
   usage pattern of database objects to optimize performance. For
   example, an index which is very heavily used can be placed on a
   very fast, highly available disk, such as an expensive solid state
   device. At the same time a table storing archived data which is
   rarely used or not performance critical could be stored on a less
   expensive, slower disk system.
  </P
><P
>   To define a tablespace, use the <A
HREF="sql-createtablespace.html"
><I
>CREATE TABLESPACE</I
></A
>
   command, for example:<A
NAME="AEN26228"
></A
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLESPACE fastspace LOCATION '/mnt/sda1/postgresql/data';</PRE
><P>
   The location must be an existing, empty directory that is owned by
   the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> system user.  All objects subsequently
   created within the tablespace will be stored in files underneath this
   directory.
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    There is usually not much point in making more than one
    tablespace per logical file system, since you cannot control the location
    of individual files within a logical file system.  However,
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does not enforce any such limitation, and
    indeed it is not directly aware of the file system boundaries on your
    system.  It just stores files in the directories you tell it to use.
   </P
></BLOCKQUOTE
></DIV
><P
>   Creation of the tablespace itself must be done as a database superuser,
   but after that you can allow ordinary database users to make use of it.
   To do that, grant them the <TT
CLASS="LITERAL"
>CREATE</TT
> privilege on it.
  </P
><P
>   Tables, indexes, and entire databases can be assigned to
   particular tablespaces. To do so, a user with the <TT
CLASS="LITERAL"
>CREATE</TT
>
   privilege on a given tablespace must pass the tablespace name as a 
   parameter to the relevant command. For example, the following creates 
   a table in the tablespace <TT
CLASS="LITERAL"
>space1</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE foo(i int) TABLESPACE space1;</PRE
><P>
  </P
><P
>   Alternatively, use the <A
HREF="runtime-config-client.html#GUC-DEFAULT-TABLESPACE"
>default_tablespace</A
> parameter:
</P><PRE
CLASS="PROGRAMLISTING"
>SET default_tablespace = space1;
CREATE TABLE foo(i int);</PRE
><P>
   When <TT
CLASS="VARNAME"
>default_tablespace</TT
> is set to anything but an empty
   string, it supplies an implicit <TT
CLASS="LITERAL"
>TABLESPACE</TT
> clause for
   <TT
CLASS="COMMAND"
>CREATE TABLE</TT
> and <TT
CLASS="COMMAND"
>CREATE INDEX</TT
> commands that
   do not have an explicit one.
  </P
><P
>   There is also a <A
HREF="runtime-config-client.html#GUC-TEMP-TABLESPACES"
>temp_tablespaces</A
> parameter, which
   determines the placement of temporary tables and indexes, as well as
   temporary files that are used for purposes such as sorting large data
   sets.  This can be a list of tablespace names, rather than only one,
   so that the load associated with temporary objects can be spread over
   multiple tablespaces.  A random member of the list is picked each time
   a temporary object is to be created.
  </P
><P
>   The tablespace associated with a database is used to store the system
   catalogs of that database.  Furthermore, it is the default tablespace
   used for tables, indexes, and temporary files created within the database,
   if no <TT
CLASS="LITERAL"
>TABLESPACE</TT
> clause is given and no other selection is
   specified by <TT
CLASS="VARNAME"
>default_tablespace</TT
> or
   <TT
CLASS="VARNAME"
>temp_tablespaces</TT
> (as appropriate).
   If a database is created without specifying a tablespace for it,
   it uses the same tablespace as the template database it is copied from.
  </P
><P
>   Two tablespaces are automatically created by <TT
CLASS="LITERAL"
>initdb</TT
>. The
   <TT
CLASS="LITERAL"
>pg_global</TT
> tablespace is used for shared system catalogs. The
   <TT
CLASS="LITERAL"
>pg_default</TT
> tablespace is the default tablespace of the
   <TT
CLASS="LITERAL"
>template1</TT
> and <TT
CLASS="LITERAL"
>template0</TT
> databases (and, therefore,
   will be the default tablespace for other databases as well, unless
   overridden by a <TT
CLASS="LITERAL"
>TABLESPACE</TT
> clause in <TT
CLASS="COMMAND"
>CREATE
   DATABASE</TT
>).
  </P
><P
>   Once created, a tablespace can be used from any database, provided
   the requesting user has sufficient privilege. This means that a tablespace
   cannot be dropped until all objects in all databases using the tablespace
   have been removed.
  </P
><P
>   To remove an empty tablespace, use the <A
HREF="sql-droptablespace.html"
><I
>DROP TABLESPACE</I
></A
>
   command.
  </P
><P
>   To determine the set of existing tablespaces, examine the
   <TT
CLASS="STRUCTNAME"
>pg_tablespace</TT
> system catalog, for example
</P><PRE
CLASS="SYNOPSIS"
>SELECT spcname FROM pg_tablespace;</PRE
><P>
   The <A
HREF="app-psql.html"
><SPAN
CLASS="APPLICATION"
>psql</SPAN
></A
> program's <TT
CLASS="LITERAL"
>\db</TT
> meta-command
   is also useful for listing the existing tablespaces.
  </P
><P
>   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> makes use of symbolic links
   to simplify the implementation of tablespaces. This
   means that tablespaces can be used <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>only</I
></SPAN
> on systems
   that support symbolic links.
  </P
><P
>   The directory <TT
CLASS="FILENAME"
>$PGDATA/pg_tblspc</TT
> contains symbolic links that
   point to each of the non-built-in tablespaces defined in the cluster.
   Although not recommended, it is possible to adjust the tablespace
   layout by hand by redefining these links.  Two warnings: do not do so
   while the server is running; and after you restart the server,
   update the <TT
CLASS="STRUCTNAME"
>pg_tablespace</TT
> catalog to show the new
   locations.  (If you do not, <TT
CLASS="LITERAL"
>pg_dump</TT
> will continue to show
   the old tablespace locations.)
  </P
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