Sophie: postgresql8.2-docs-8.2.14-1mdv2010.0 i586

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><A
NAME="MANAGE-AG-TABLESPACES"
>19.6. Tablespaces</A
></H1
><A
NAME="AEN22965"
></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="AEN22974"
></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
>    The tablespace associated with a database is used to store the system
    catalogs of that database, as well as any temporary files created by
    server processes using that database.  Furthermore, it is the default
    tablespace selected for tables and indexes created within the database,
    if no <TT
CLASS="LITERAL"
>TABLESPACE</TT
> clause is given (either explicitly or via
    <TT
CLASS="VARNAME"
>default_tablespace</TT
>) when the objects are created.
    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 extensive 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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