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Rename the built-in tablespaces to pg_default and pg_global, and prohibit

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creation of user-defined tablespaces with names starting with 'pg_', as
per suggestion of Chris K-L.  Also install admin-guide tablespace
documentation from Gavin.
This commit is contained in:
Tom Lane
2004-06-21 04:06:07 +00:00
parent 483b7f8249
commit f5f448fb3e
7 changed files with 140 additions and 117 deletions
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15
doc/src/sgml/diskusage.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/diskusage.sgml,v 1.10 2003/11/29 19:51:36 pgsql Exp $
$PostgreSQL: pgsql/doc/src/sgml/diskusage.sgml,v 1.11 2004/06/21 04:06:03 tgl Exp $
-->
<chapter id="diskusage">
@ -124,20 +124,15 @@ SELECT relname, relpages FROM pg_class ORDER BY relpages DESC;
<para>
If you cannot free up additional space on the disk by deleting
other things you can move some of the database files to other file
systems and create a symlink from the original location. But
note that <application>pg_dump</> cannot save the location layout
information of such a setup; a restore would put everything back in
one place. To avoid running out of disk space, you can place the
WAL files or individual databases in other locations while creating
them. See the <command>initdb</> documentation and <xref
linkend="manage-ag-alternate-locs"> for more information about that.
other things, you can move some of the database files to other file
systems by making use of tablespaces. See <xref
linkend="manage-ag-tablespaces"> for more information about that.
</para>
<tip>
<para>
Some file systems perform badly when they are almost full, so do
not wait until the disk is full to take action.
not wait until the disk is completely full to take action.
</para>
</tip>
</sect1>

192
doc/src/sgml/manage-ag.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/manage-ag.sgml,v 2.30 2004/06/18 06:13:02 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/manage-ag.sgml,v 2.31 2004/06/21 04:06:03 tgl Exp $
-->
<chapter id="managing-databases">
@ -295,86 +295,6 @@ ALTER DATABASE mydb SET geqo TO off;
</para>
</sect1>
<sect1 id="manage-ag-alternate-locs">
<title>Alternative Locations</title>
<para>
XXX this is entirely dead now, and needs to be replaced by a DBA-level
description of tablespaces.
</para>
<para>
It is possible to create a database in a location other than the
default location for the installation. But remember that all database access
occurs through the
database server, so any location specified must be
accessible by the server.
</para>
<para>
Alternative database locations are referenced by an environment
variable which gives the absolute path to the intended storage
location. This environment variable must be present in the server's
environment, so it must have been defined before the server
was started. (Thus, the set of available alternative locations is
under the site administrator's control; ordinary users can't
change it.) Any valid environment variable name may
be used to reference an alternative location, although using
variable names with a prefix of <literal>PGDATA</> is recommended
to avoid confusion and conflict with other variables.
</para>
<para>
To create the variable in the environment of the server process
you must first shut down the server, define the variable,
initialize the data area, and finally restart the server. (See also
<xref linkend="postmaster-shutdown"> and <xref
linkend="postmaster-start">.) To set an environment variable, type
<programlisting>
PGDATA2=/home/postgres/data
export PGDATA2
</programlisting>
in Bourne shells, or
<programlisting>
setenv PGDATA2 /home/postgres/data
</programlisting>
in <command>csh</> or <command>tcsh</>. You have to make sure that this environment
variable is always defined in the server environment, otherwise
you won't be able to access that database. Therefore you probably
want to set it in some sort of shell start-up file or server
start-up script.
</para>
<para>
<indexterm><primary>initlocation</></>
To create a data storage area in <envar>PGDATA2</>, ensure that
the containing directory (here, <filename>/home/postgres</filename>)
already exists and is writable
by the user account that runs the server (see <xref
linkend="postgres-user">). Then from the command line, type
<programlisting>
initlocation PGDATA2
</programlisting>
(<emphasis>not</emphasis> <literal>initlocation
$PGDATA2</literal>). Then you can restart the server.
</para>
<para>
To create a database within the new location, use the command
<synopsis>
CREATE DATABASE <replaceable>name</> WITH LOCATION '<replaceable>location</>';
</synopsis>
where <replaceable>location</> is the environment variable you
used, <envar>PGDATA2</> in this example. The <command>createdb</>
command has the option <option>-D</> for this purpose.
</para>
<para>
Databases created in alternative locations can be
accessed and dropped like any other database.
</para>
</sect1>
<sect1 id="manage-ag-dropdb">
<title>Destroying a Database</title>
@ -410,6 +330,116 @@ dropdb <replaceable class="parameter">dbname</replaceable>
the database with the current user name.)
</para>
</sect1>
<sect1 id="manage-ag-tablespaces">
<title>Tablespaces</title>
<para>
Tablespaces in <productname>PostgreSQL</> allow database superusers 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.
</para>
<para>
By using tablespaces, a database administrator can control the disk
layout of a <productname>PostgreSQL</> installation. This is useful in
at least two ways. Firstly, if the partition or volume on which the cluster
was initialized runs out of space and cannot be extended logically
or otherwise, a tablespace can be created on a different partition
and used until the system can be reconfigured.
</para>
<para>
Secondly, tablespaces allow a database administrator to arrange data
locations based on the usage patterns of database objects. For
example, an index which is very heavily used can be placed on 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.
</para>
<para>
Databases, schemas, tables, indexes and sequences can all be placed in
particular tablespaces. To do so, a user with the <literal>CREATE</>
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 <literal>space1</>:
<programlisting>
CREATE TABLE foo(i int) TABLESPACE space1;
</programlisting>
</para>
<para>
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 any objects created within the database, if
no specific <literal>TABLESPACE</> clause is given when those 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.
</para>
<para>
A schema does not in itself occupy any storage (other than a system
catalog entry), so assigning a tablespace to a schema does not in itself
do anything. What this actually does is to set a default tablespace
for tables, indexes, and sequences later created within the schema. If
no tablespace is mentioned when creating a schema, it inherits its
default tablespace from the current database.
</para>
<para>
The default choice of tablespace for an index is the same tablespace
already assigned to the table the index is for.
</para>
<para>
Another way to state the above rules is that when a schema, table, index
or sequence is created without specifying a tablespace, the object
inherits its logical parent's tablespace. A schema will be created in the
current database's tablespace; a table or sequence will be created in the
tablespace of the schema it is being created in; an index will be created
in the tablespace of the table underlying the index.
</para>
<para>
Two tablespaces are automatically created by <literal>initdb</>. The
<literal>pg_global</> tablespace is used for shared system catalogs. The
<literal>pg_default</> tablespace is the default tablespace of the
<literal>template1</> and <literal>template0</> databases (and, therefore,
will be the default tablespace for everything else as well, unless
explicit <literal>TABLESPACE</> clauses are used somewhere along the
line).
</para>
<para>
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.
</para>
<para>
To simplify the implementation of tablespaces,
<productname>PostgreSQL</> makes extensive use of symbolic links. This
means that tablespaces can be used <emphasis>only</> on systems
that support symbolic links.
</para>
<para>
The directory <filename>$PGDATA/pg_tblspc</> 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 postmaster is running; and after you restart the postmaster,
update the <structname>pg_tablespace</> catalog to show the new
locations. (If you do not, <literal>pg_dump</> will continue to show
the old tablespace locations.)
</para>
</sect1>
</chapter>
<!-- Keep this comment at the end of the file

14
doc/src/sgml/ref/postmaster.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.49 2004/03/23 06:09:00 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.50 2004/06/21 04:06:04 tgl Exp $
PostgreSQL documentation
-->
@ -417,18 +417,6 @@ PostgreSQL documentation
</listitem>
</varlistentry>
<varlistentry>
<term>others</term>
<listitem>
<para>
Other environment variables may be used to designate alternative
data storage locations. See <xref linkend="manage-ag-alternate-locs"> for more
information.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>