Properly indent tablespace SGML section.
This commit is contained in:
Bruce Momjian
parent
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/manage-ag.sgml,v 2.54 2007/06/03 17:05:52 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/manage-ag.sgml,v 2.55 2007/11/04 19:43:33 momjian Exp $ -->
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<chapter id="managing-databases">
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<title>Managing Databases</title>
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@ -344,156 +344,156 @@ dropdb <replaceable class="parameter">dbname</replaceable>
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<primary>tablespace</primary>
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</indexterm>
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<para>
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Tablespaces in <productname>PostgreSQL</> allow database administrators to
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define locations in the file system where the files representing
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database objects can be stored. Once created, a tablespace can be referred
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to by name when creating database objects.
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</para>
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<para>
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Tablespaces in <productname>PostgreSQL</> allow database administrators to
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define locations in the file system where the files representing
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database objects can be stored. Once created, a tablespace can be referred
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to by name when creating database objects.
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</para>
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<para>
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By using tablespaces, an administrator can control the disk layout
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of a <productname>PostgreSQL</> installation. This is useful in at
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least two ways. First, if the partition or volume on which the
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cluster was initialized runs out of space and cannot be extended,
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a tablespace can be created on a different partition and used
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until the system can be reconfigured.
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</para>
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<para>
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By using tablespaces, an administrator can control the disk layout
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of a <productname>PostgreSQL</> installation. This is useful in at
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least two ways. First, if the partition or volume on which the
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cluster was initialized runs out of space and cannot be extended,
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a tablespace can be created on a different partition and used
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until the system can be reconfigured.
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</para>
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<para>
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Second, tablespaces allow an administrator to use knowledge of the
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usage pattern of database objects to optimize performance. For
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example, an index which is very heavily used can be placed on a
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very fast, highly available disk, such as an expensive solid state
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device. At the same time a table storing archived data which is
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rarely used or not performance critical could be stored on a less
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expensive, slower disk system.
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</para>
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<para>
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Second, tablespaces allow an administrator to use knowledge of the
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usage pattern of database objects to optimize performance. For
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example, an index which is very heavily used can be placed on a
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very fast, highly available disk, such as an expensive solid state
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device. At the same time a table storing archived data which is
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rarely used or not performance critical could be stored on a less
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expensive, slower disk system.
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</para>
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<para>
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To define a tablespace, use the <xref
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linkend="sql-createtablespace" endterm="sql-createtablespace-title">
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command, for example:<indexterm><primary>CREATE TABLESPACE</></>:
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<para>
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To define a tablespace, use the <xref
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linkend="sql-createtablespace" endterm="sql-createtablespace-title">
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command, for example:<indexterm><primary>CREATE TABLESPACE</></>:
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<programlisting>
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CREATE TABLESPACE fastspace LOCATION '/mnt/sda1/postgresql/data';
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</programlisting>
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The location must be an existing, empty directory that is owned by
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the <productname>PostgreSQL</> system user. All objects subsequently
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created within the tablespace will be stored in files underneath this
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directory.
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</para>
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<note>
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<para>
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There is usually not much point in making more than one
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tablespace per logical file system, since you cannot control the location
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of individual files within a logical file system. However,
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<productname>PostgreSQL</> does not enforce any such limitation, and
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indeed it is not directly aware of the file system boundaries on your
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system. It just stores files in the directories you tell it to use.
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</para>
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</note>
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The location must be an existing, empty directory that is owned by
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the <productname>PostgreSQL</> system user. All objects subsequently
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created within the tablespace will be stored in files underneath this
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directory.
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</para>
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<note>
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<para>
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Creation of the tablespace itself must be done as a database superuser,
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but after that you can allow ordinary database users to make use of it.
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To do that, grant them the <literal>CREATE</> privilege on it.
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There is usually not much point in making more than one
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tablespace per logical file system, since you cannot control the location
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of individual files within a logical file system. However,
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<productname>PostgreSQL</> does not enforce any such limitation, and
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indeed it is not directly aware of the file system boundaries on your
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system. It just stores files in the directories you tell it to use.
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</para>
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</note>
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<para>
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Tables, indexes, and entire databases can be assigned to
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particular tablespaces. To do so, a user with the <literal>CREATE</>
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privilege on a given tablespace must pass the tablespace name as a
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parameter to the relevant command. For example, the following creates
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a table in the tablespace <literal>space1</>:
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<para>
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Creation of the tablespace itself must be done as a database superuser,
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but after that you can allow ordinary database users to make use of it.
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To do that, grant them the <literal>CREATE</> privilege on it.
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</para>
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<para>
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Tables, indexes, and entire databases can be assigned to
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particular tablespaces. To do so, a user with the <literal>CREATE</>
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privilege on a given tablespace must pass the tablespace name as a
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parameter to the relevant command. For example, the following creates
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a table in the tablespace <literal>space1</>:
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<programlisting>
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CREATE TABLE foo(i int) TABLESPACE space1;
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</programlisting>
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</para>
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</para>
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<para>
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Alternatively, use the <xref linkend="guc-default-tablespace"> parameter:
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<para>
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Alternatively, use the <xref linkend="guc-default-tablespace"> parameter:
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<programlisting>
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SET default_tablespace = space1;
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CREATE TABLE foo(i int);
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</programlisting>
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When <varname>default_tablespace</> is set to anything but an empty
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string, it supplies an implicit <literal>TABLESPACE</> clause for
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<command>CREATE TABLE</> and <command>CREATE INDEX</> commands that
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do not have an explicit one.
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</para>
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When <varname>default_tablespace</> is set to anything but an empty
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string, it supplies an implicit <literal>TABLESPACE</> clause for
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<command>CREATE TABLE</> and <command>CREATE INDEX</> commands that
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do not have an explicit one.
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</para>
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<para>
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There is also a <xref linkend="guc-temp-tablespaces"> parameter, which
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determines the placement of temporary tables and indexes, as well as
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temporary files that are used for purposes such as sorting large data
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sets. This can be a list of tablespace names, rather than only one,
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so that the load associated with temporary objects can be spread over
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multiple tablespaces. A random member of the list is picked each time
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a temporary object is to be created.
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</para>
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<para>
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There is also a <xref linkend="guc-temp-tablespaces"> parameter, which
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determines the placement of temporary tables and indexes, as well as
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temporary files that are used for purposes such as sorting large data
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sets. This can be a list of tablespace names, rather than only one,
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so that the load associated with temporary objects can be spread over
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multiple tablespaces. A random member of the list is picked each time
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a temporary object is to be created.
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</para>
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<para>
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The tablespace associated with a database is used to store the system
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catalogs of that database. Furthermore, it is the default tablespace
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used for tables, indexes, and temporary files created within the database,
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if no <literal>TABLESPACE</> clause is given and no other selection is
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specified by <varname>default_tablespace</> or
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<varname>temp_tablespaces</> (as appropriate).
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If a database is created without specifying a tablespace for it,
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it uses the same tablespace as the template database it is copied from.
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</para>
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<para>
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The tablespace associated with a database is used to store the system
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catalogs of that database. Furthermore, it is the default tablespace
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used for tables, indexes, and temporary files created within the database,
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if no <literal>TABLESPACE</> clause is given and no other selection is
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specified by <varname>default_tablespace</> or
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<varname>temp_tablespaces</> (as appropriate).
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If a database is created without specifying a tablespace for it,
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it uses the same tablespace as the template database it is copied from.
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</para>
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<para>
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Two tablespaces are automatically created by <literal>initdb</>. The
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<literal>pg_global</> tablespace is used for shared system catalogs. The
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<literal>pg_default</> tablespace is the default tablespace of the
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<literal>template1</> and <literal>template0</> databases (and, therefore,
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will be the default tablespace for other databases as well, unless
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overridden by a <literal>TABLESPACE</> clause in <command>CREATE
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DATABASE</>).
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</para>
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<para>
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Two tablespaces are automatically created by <literal>initdb</>. The
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<literal>pg_global</> tablespace is used for shared system catalogs. The
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<literal>pg_default</> tablespace is the default tablespace of the
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<literal>template1</> and <literal>template0</> databases (and, therefore,
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will be the default tablespace for other databases as well, unless
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overridden by a <literal>TABLESPACE</> clause in <command>CREATE
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DATABASE</>).
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</para>
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<para>
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Once created, a tablespace can be used from any database, provided
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the requesting user has sufficient privilege. This means that a tablespace
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cannot be dropped until all objects in all databases using the tablespace
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have been removed.
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</para>
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<para>
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Once created, a tablespace can be used from any database, provided
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the requesting user has sufficient privilege. This means that a tablespace
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cannot be dropped until all objects in all databases using the tablespace
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have been removed.
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</para>
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<para>
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To remove an empty tablespace, use the <xref
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linkend="sql-droptablespace" endterm="sql-droptablespace-title">
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command.
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</para>
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<para>
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To remove an empty tablespace, use the <xref
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linkend="sql-droptablespace" endterm="sql-droptablespace-title">
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command.
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</para>
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<para>
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To determine the set of existing tablespaces, examine the
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<structname>pg_tablespace</> system catalog, for example
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<para>
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To determine the set of existing tablespaces, examine the
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<structname>pg_tablespace</> system catalog, for example
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<synopsis>
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SELECT spcname FROM pg_tablespace;
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</synopsis>
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The <xref linkend="app-psql"> program's <literal>\db</> meta-command
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is also useful for listing the existing tablespaces.
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</para>
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The <xref linkend="app-psql"> program's <literal>\db</> meta-command
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is also useful for listing the existing tablespaces.
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</para>
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<para>
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<productname>PostgreSQL</> makes use of symbolic links
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to simplify the implementation of tablespaces. This
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means that tablespaces can be used <emphasis>only</> on systems
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that support symbolic links.
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</para>
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<para>
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<productname>PostgreSQL</> makes use of symbolic links
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to simplify the implementation of tablespaces. This
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means that tablespaces can be used <emphasis>only</> on systems
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that support symbolic links.
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</para>
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<para>
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The directory <filename>$PGDATA/pg_tblspc</> contains symbolic links that
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point to each of the non-built-in tablespaces defined in the cluster.
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Although not recommended, it is possible to adjust the tablespace
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layout by hand by redefining these links. Two warnings: do not do so
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while the server is running; and after you restart the server,
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update the <structname>pg_tablespace</> catalog to show the new
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locations. (If you do not, <literal>pg_dump</> will continue to show
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the old tablespace locations.)
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</para>
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<para>
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The directory <filename>$PGDATA/pg_tblspc</> contains symbolic links that
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point to each of the non-built-in tablespaces defined in the cluster.
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Although not recommended, it is possible to adjust the tablespace
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layout by hand by redefining these links. Two warnings: do not do so
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while the server is running; and after you restart the server,
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update the <structname>pg_tablespace</> catalog to show the new
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locations. (If you do not, <literal>pg_dump</> will continue to show
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the old tablespace locations.)
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</para>
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</sect1>
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</chapter>
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