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docs: tablespaces cannot be accessed independently

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Mention impossibility of moving tablespaces, backing them up
independently, or the inadvisability of placing them on temporary
file systems.

Patch by Craig Ringer, adjustments by Ian Lawrence Warwick and me
This commit is contained in:
Bruce Momjian 2014-04-19 10:52:49 -04:00
parent 13ecb822e8
commit 4353d1809f
2 changed files with 27 additions and 2 deletions
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21
doc/src/sgml/manage-ag.sgml
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@ -379,17 +379,34 @@ dropdb <replaceable class="parameter">dbname</replaceable>
expensive, slower disk system. expensive, slower disk system.
</para> </para>
<warning>
<para>
Even though located outside the main PostgreSQL data directory,
tablespaces are an integral part of the database cluster and
<emphasis>cannot</emphasis> be treated as an autonomous collection
of data files. They are dependent on metadata contained in the main
data directory, and therefore cannot be attached to a different
database cluster or backed up individually. Similarly, if you lose
a tablespace (file deletion, disk failure, etc), the database cluster
might become unreadable or unable to start. Placing a tablespace
on a temporary file system like a ramdisk risks the reliability of
the entire cluster.
</para>
</warning>
<para> <para>
To define a tablespace, use the <xref To define a tablespace, use the <xref
linkend="sql-createtablespace"> linkend="sql-createtablespace">
command, for example:<indexterm><primary>CREATE TABLESPACE</></>: command, for example:<indexterm><primary>CREATE TABLESPACE</></>:
<programlisting> <programlisting>
CREATE TABLESPACE fastspace LOCATION '/mnt/sda1/postgresql/data'; CREATE TABLESPACE fastspace LOCATION '/ssd1/postgresql/data';
</programlisting> </programlisting>
The location must be an existing, empty directory that is owned by The location must be an existing, empty directory that is owned by
the <productname>PostgreSQL</> operating system user. All objects subsequently the <productname>PostgreSQL</> operating system user. All objects subsequently
created within the tablespace will be stored in files underneath this created within the tablespace will be stored in files underneath this
directory. directory. The location must not be on removable or transient storage,
as the cluster might fail to function if the tablespace is missing
or lost.
</para> </para>
<note> <note>

8
doc/src/sgml/ref/create_tablespace.sgml
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@ -50,6 +50,14 @@ CREATE TABLESPACE <replaceable class="parameter">tablespace_name</replaceable>
<command>CREATE INDEX</> or <command>ADD CONSTRAINT</> to have the data <command>CREATE INDEX</> or <command>ADD CONSTRAINT</> to have the data
files for these objects stored within the specified tablespace. files for these objects stored within the specified tablespace.
</para> </para>
<warning>
<para>
A tablespace cannot be used independently of the cluster in which it
is defined; see <xref linkend="manage-ag-tablespaces"/>.
</para>
</warning>
</refsect1> </refsect1>
<refsect1> <refsect1>