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New and revised material for Admin guide, re backup & restore and database

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management
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Peter Eisentraut 2000-06-30 16:14:21 +00:00
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doc/src/sgml/admin.sgml
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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/admin.sgml,v 1.23 2000/06/18 21:24:51 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/admin.sgml,v 1.24 2000/06/30 16:14:21 petere Exp $
Postgres Administrator's Guide.
Derived from postgres.sgml.
@ -21,16 +21,15 @@ Derived from postgres.sgml.
<!entity install SYSTEM "install.sgml">
<!entity installw SYSTEM "install-win32.sgml">
<!entity layout SYSTEM "layout.sgml">
<!entity manage-ag SYSTEM "manage-ag.sgml">
<!entity ports SYSTEM "ports.sgml">
<!entity recovery SYSTEM "recovery.sgml">
<!entity regress SYSTEM "regress.sgml">
<!entity release SYSTEM "release.sgml">
<!entity runtime SYSTEM "runtime.sgml">
<!entity client-auth SYSTEM "client-auth.sgml">
<!entity manage-ag SYSTEM "manage-ag.sgml">
<!entity user-manag SYSTEM "user-manag.sgml">
<!entity start-ag SYSTEM "start-ag.sgml">
<!entity trouble SYSTEM "trouble.sgml">
<!entity backup SYSTEM "backup.sgml">
<!entity recovery SYSTEM "recovery.sgml">
<!entity regress SYSTEM "regress.sgml">
<!entity biblio SYSTEM "biblio.sgml">
]>
@ -113,9 +112,9 @@ Your name here...
&installw;
&runtime;
&client-auth;
&user-manag;
&start-ag;
&manage-ag;
&user-manag;
&backup;
&recovery;
&regress;
&release;

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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/backup.sgml,v 2.1 2000/06/30 16:14:21 petere Exp $ -->
<chapter id="backup">
<title>Backup and Restore</title>
<para>
As everything that contains valuable data, <productname>Postgres</>
databases should be backed up regularly. While the procedure is
essentially simple, it is important to have a basic understanding of
the underlying techniques and assumptions.
</para>
<para>
There are two fundamentally different approaches to backing up
<productname>Postgres</> data:
<itemizedlist>
<listitem><para><acronym>SQL</> dump</para></listitem>
<listitem><para>File system level backup</para></listitem>
</itemizedlist>
</para>
<sect1>
<title><acronym>SQL</> Dump</title>
<para>
The idea behind this method is to generate a text file with SQL
commands that, when fed back to the server, will recreate the
database in the same state as it was at the time of the dump.
<productname>Postgres</> provides the utility program
<application>pg_dump</> for this purpose. The basic usage of this
command is:
<synopsis>
pg_dump <replaceable class="parameter">dbname</replaceable> &gt; <replaceable class="parameter">outfile</replaceable>
</synopsis>
As you see, <application>pg_dump</> writes its results to the
standard output. We will see below how this can be useful.
</para>
<para>
<application>pg_dump</> is a regular <productname>Postgres</>
client application (albeit a particularly clever one). This means
that you can do this backup procedure from any remote host that has
access to the database. But remember that <application>pg_dump</>
does not operate with special permissions. In particular, you must
have read access to all tables that you want to back up, so in
practice you almost always have to be a database superuser.
</para>
<para>
To specify which databaser server <application>pg_dump</> should
contact, use the command line options <option>-h
<replaceable>host</></> and <option>-p <replaceable>port</></>. The
default host is the local host or whatever your
<envar>PGHOST</envar> environment variable specifies. Similarly,
the default port is indicated by the <envar>PGPORT</envar>
environment variable or, failing that, by the compiled-in default.
(Conveniently, the server will normally have the same compiled-in
default.)
</para>
<para>
As any other <productname>Postgres</> client application,
<application>pg_dump</> will by default connect with the database
user name that is equal to the current Unix user name. To override
this, either specify the <option>-u</option> option to force a prompt for
the user name, or set the environment variable
<envar>PGUSER</envar>. Remember that <application>pg_dump</>
connections are subject to the normal client authentication
mechanisms (which are described in <xref
linkend="client-authentication">).
</para>
<para>
Dumps created by <application>pg_dump</> are internally consistent,
that is, updates to the database while <application>pg_dump</> is
running will not be in the dump. <application>pg_dump</> does not
block other operations on the database while it is working.
(Exceptions are those operations that need to operate with an
exclusive lock, such as <command>VACUUM</command>.)
</para>
<important>
<para>
When your database schema relies on OIDs (for instances as foreign
keys) you must instruct <application>pg_dump</> to dump the OIDs
as well. To do this, use the <option>-o</option> command line
option.
</para>
</important>
<sect2>
<title>Restoring the dump</title>
<para>
The text files created by <application>pg_dump</> are intended to
be read in by the <application>psql</application> program. The
general command form to restore a dump is
<synopsis>
psql <replaceable class="parameter">dbname</replaceable> &lt; <replaceable class="parameter">infile</replaceable>
</synopsis>
where <replaceable class="parameter">infile</replaceable> is what
you used as <replaceable class="parameter">outfile</replaceable>
for the pg_dump command. The database <replaceable
class="parameter">dbname</replaceable> will not be created by this
command, you must do that yourself before executing
<application>psql</> (e.g., with <userinput>createdb <replaceable
class="parameter">dbname</></userinput>). <application>psql</>
supports similar options to <application>pg_dump</> for
controlling the database server location and the user names. See
its reference page for more information.
</para>
<para>
If the objects in the original database were owned by different
users, then the dump will instruct <application>psql</> to connect
as each affected user in turn and then create the relevant
objects. This way the original ownership is preserved. This also
means, however, that all these user must already exist, and
furthermore that you must be allowed to connect as each of them.
It might therefore be necessary to temporarily relax the client
authentication settings.
</para>
<para>
The ability of <application>pg_dump</> and <application>psql</> to
write or read from pipes also make it possible to dump a database
directory from one server to another, for example
<informalexample>
<programlisting>
pg_dump -h <replaceable>host1</> <replaceable>dbname</> | psql -h <replaceable>host2</> <replaceable>dbname</>
</programlisting>
</informalexample>
</para>
</sect2>
<sect2>
<title>Using <command>pg_dumpall</></title>
<para>
The above mechanism is cumbersome and inappropriate when backing
up an entire database cluster. For this reason the
<application>pg_dumpall</> program is provided.
<application>pg_dumpall</> backs up each database in a given
cluster and also makes sure that the state of global data such as
users and groups is preserved. The call sequence for
<application>pg_dumpall</> is simply
<synopsis>
pg_dumpall &gt; <replaceable>outfile</>
</synopsis>
The resulting dumps can be restored with <application>psql</> as
described above. But in this case it is definitely necessary that
you have database superuser access, as that is required to restore
the user and group information.
</para>
<para>
<application>pg_dumpall</application> has one little flaw: It is
not prepared for interactively authenticating to each database it
dumps. If you are using password authentication then you need to
set it the environment variable <envar>PGPASSWORD</envar> to
communicate the password the the underlying calls to
<application>pg_dump</>. More severely, if you have different
passwords set up for each database, then
<application>pg_dumpall</> will fail. You can either choose a
different authentication mechanism for the purposes of backup or
adjust the <filename>pg_dumpall</filename> shell script to your
needs.
</para>
</sect2>
<sect2>
<title>Large Databases</title>
<note>
<title>Acknowledgement</title>
<para>
Originally written by Hannu Krosing
(<email>hannu@trust.ee</email>) on 1999-06-19
</para>
</note>
<para>
Since <productname>Postgres</productname> allows tables larger
than the maximum file size on your system, it can be problematic
to dump the table to a file, since the resulting file will likely
be larger than the maximum size allowed by your system. As
<application>pg_dump</> writes to the standard output, you can
just use standard *nix tools to work around this possible problem.
</para>
<formalpara>
<title>Use compressed dumps.</title>
<para>
Use your favorite compression program, for example
<application>gzip</application>.
<programlisting>
pg_dump <replaceable class="parameter">dbname</replaceable> | gzip &gt; <replaceable class="parameter">filename</replaceable>.gz
</programlisting>
Reload with
<programlisting>
createdb <replaceable class="parameter">dbname</replaceable>
gunzip -c <replaceable class="parameter">filename</replaceable>.gz | psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
or
<programlisting>
cat <replaceable class="parameter">filename</replaceable>.gz | gunzip | psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
</para>
</formalpara>
<formalpara>
<title>Use <application>split</>.</title>
<para>
This allows you to split the output into pieces that are
acceptable in size to the underlying file system. For example, to
make chunks of 1 megabyte:
<informalexample>
<programlisting>
pg_dump <replaceable class="parameter">dbname</replaceable> | split -b 1m - <replaceable class="parameter">filename</replaceable>
</programlisting>
</informalexample>
Reload with
<informalexample>
<programlisting>
createdb <replaceable class="parameter">dbname</replaceable>
cat <replaceable class="parameter">filename</replaceable>.* | psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
</informalexample>
</para>
</formalpara>
</sect2>
<sect2>
<title>Caveats</title>
<para>
<application>pg_dump</> (and by implication
<application>pg_dumpall</>) has a few limitations which stem from
the difficulty to reconstruct certain information from the system
catalogs.
</para>
<para>
Specifically, the order in which <application>pg_dump</> writes
the objects is not very sophisticated. This can lead to problems
for example when functions are used as column default values. The
only answer is to manually reorder the dump. If you created
circular dependencies in your schema then you will have more work
to do.
</para>
<para>
Large objects are not handled by <application>pg_dump</>. The
directory <filename>contrib/pg_dumplo</> of the
<productname>Postgres</> source tree contains a program that can
do that.
</para>
<para>
Please familiarize yourself with the
<citerefentry><refentrytitle>pg_dump</></> reference page.
</para>
</sect2>
</sect1>
<sect1>
<title>File system level backup</title>
<para>
An alternative backup strategy is to directly copy the files that
<productname>Postgres</> uses to store the data in the database. In
<xref linkend="creating-cluster"> it is explained where these files
are located, but you have probably found them already if you are
interested in this method. You can use whatever method you prefer
for doing usual file system backups, for example
<informalexample>
<programlisting>
tar -cf backup.tar /usr/local/pgsql/data
</programlisting>
</informalexample>
</para>
<para>
There are two restrictions, however, which make this method
impractical, or at least inferior to the <application>pg_dump</>
method:
<orderedlist>
<listitem>
<para>
The database server <emphasis>must</> be shut down in order to
get a usable backup. Half-way measures such as disallowing all
connections will not work as there is always some buffering
going on. For this reason it is also not advisable to trust file
systems that claim to support <quote>consistent
snapshots</quote>. Information about stopping the server can be
found in <xref linkend="postmaster-shutdown">.
</para>
<para>
Needless to say that you also need to shut down the server
before restoring the data.
</para>
</listitem>
<listitem>
<para>
If you have dug into the details of the file system layout you
may be tempted to try to back up or restore only certain
individual tables or databases from their respective files or
directories. This will <emphasis>not</> work because the
information contained in these files contains only half the
truth. The other half is in the file
<filename>pg_log</filename>, which contains the commit status of
all transactions. A table file is only usable with this
information. Of course it is also impossible to restore only a
table and the associated <filename>pg_log</filename> file
because that will render all other tables in the database
cluster useless.
</para>
</listitem>
</orderedlist>
</para>
<para>
Also note that the file system backup will not necessarily be
smaller than an SQL dump. On the contrary, it will most likely be
larger. (<application>pg_dump</application> does not need to dump
the contents of indices for example, just the commands to recreate
them.)
</para>
</sect1>
<sect1>
<title>Migration between releases</title>
<para>
As a general rule, the internal data storage format is subject to
change between releases of <productname>Postgres</>. This does not
apply to different <quote>patch levels</quote>, these always have
compatible storage formats. For example, releases 6.5.3, 7.0.1, and
7.1 are not compatible, whereas 7.0.2 and 7.0.1 are. When you
update between compatible versions, then you can simply reuse the
data area in disk by the new executables. Otherwise you need to
<quote>back up</> your data and <quote>restore</> it on the new
server, using <application>pg_dump</>. (There are checks in place
that prevent you from doing the wrong thing, so no harm can be done
by confusing these things.) The precise installation procedure is
not subject of this section, the <citetitle>Installation
Instructions</citetitle> carry these details.
</para>
<para>
The least downtime can be achieved by installing the new server in
a different directory and running both the old and the new servers
in parallel, on different ports. Then you can use something like
<informalexample>
<programlisting>
pg_dumpall -p 5432 | psql -d template1 -p 6543
</programlisting>
</informalexample>
to transfer your data, or use an intermediate file if you want.
Then you can shut down the old server and start the new server at
the port the old one was running at. You should make sure that the
database is not updated after you run <application>pg_dumpall</>,
otherwise you will obviously lose that data. See <xref
linkend="client-authentication"> for information on how to prohibit
access. In practice you probably want to test your client
applications on the new setup before switching over.
</para>
<para>
If you cannot or do not want to run two servers in parallel you can
do the back up step before installing the new version, bring down
the server, move the old version out of the way, install the new
version, start the new server, restore the data. For example:
<informalexample>
<programlisting>
pg_dumpall > backup
kill -INT `cat /usr/local/pgsql/postmaster.pid`
mv /usr/local/pgsql /usr/local/pgsql.old
cd /usr/src/postgresql-7.1
gmake install
initdb -D /usr/local/pgsql/data
postmaster -D /usr/local/pgsql/data
psql < backup
</programlisting>
</informalexample>
See <xref linkend="runtime"> about ways to start and stop the
server and other details. The installation instructions will advise
you of strategic places to perform these steps.
</para>
<note>
<para>
When you <quote>move the old installation out of the way</quote>
it is no longer perfectly usable. Some parts of the installation
contain information about where the other parts are located. This
is usually not a big problem but if you plan on using two
installations in parallel for a while you should assign them
different installation directories at build time.
</para>
</note>
</sect1>
</chapter>

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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/manage-ag.sgml,v 2.8 2000/05/02 20:01:52 thomas Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/manage-ag.sgml,v 2.9 2000/06/30 16:14:21 petere Exp $
-->
<chapter id="manage-ag">
<title>Managing a Database</title>
<chapter id="managing-databases">
<title>Managing Databases</title>
<para>
A database is a named collection of SQL objects (<quote>database
objects</quote>); every database object (tables, function, etc.)
belongs to one and only one database. An application that connects
to the database server specifies with its connection request the
name of the database it wants to connect to. It is not possible to
access more than once database per connection. (But an application
is not restricted in the number of connections it opens to the same
or other databases.)
</para>
<note>
<para>
<acronym>SQL</> calls databases <quote>catalogs</>, but there is no
difference in practice.
</para>
</note>
<para>
In order to create or drop databases, the <productname>Postgres</>
<application>postmaster</> must be up and running (see <xref
linkend="postmaster-start">).
</para>
<sect1>
<title>Creating a Database</title>
<para>
If the <productname>Postgres</productname>
<application>postmaster</application> is up and running we can create
some databases to experiment with. Here, we describe the
basic commands for managing a database.
Databases are created with the query language command
<command>CREATE DATABASE</command>:
<synopsis>
CREATE DATABASE <replaceable>name</>
</synopsis>
where <replaceable>name</> can be chosen freely. (Depending on the
current implementation, certain characters that are special to the
underlying operating system might be prohibited. There will be
run-time checks for that.) The current user automatically becomes
the owner of the new database. It is the privilege of the owner of
a database to remove it later on (which also removes all the
objects in it, even if they have a different owner).
</para>
<sect1>
<title>Creating a Database</title>
<para>
The creation of databases is a restricted operation. See <xref
linkend="user-attributes"> how to grant permission.
</para>
<formalpara>
<title>Bootstrapping</title>
<para>
Let's say you want to create a database named mydb.
You can do this with the following command:
<programlisting>
% createdb <replaceable class="parameter">dbname</replaceable>
</programlisting>
<productname>Postgres</productname> allows you to create
any number of databases
at a given site and you automatically become the
database administrator of the database you just created.
Database names must have an alphabetic first
character and are limited to 31 characters in length.
Not every user has authorization to become a database
administrator. If <productname>Postgres</productname>
refuses to create databases
for you, then the site administrator needs to grant you
permission to create databases. Consult your site
administrator if this occurs.
Since you need to be connected to the database server in order to
execute the <command>CREATE DATABASE</command> command, the
question remains how the <emphasis>first</> database at any given
site can be created. The first database is always created by the
<command>initdb</> command when the data storage area is
initialized. (See <xref linkend="creating-cluster">.) This
database is called <literal>template1</> and cannot be deleted. So
to create the first <quote>real</> database you can connect to
<literal>template1</>.
</para>
</sect1>
</formalpara>
<sect1>
<title>Accessing a Database</title>
<para>
The name <quote>template1</quote> is no accident: When a new
database is created, the template database is essentially cloned.
This means that any changes you make in <literal>template1</> are
propagated to all subsequently created databases. This implies that
you should not use the template database for real work, but when
used judiciously this feature can be convenient.
</para>
<para>
As an extra convenience, there is also a program that you can
execute from the shell to create new databases,
<filename>createdb</>.
<synopsis>
createdb <replaceable class="parameter">dbname</replaceable>
</synopsis>
<filename>createdb</> does no magic. It connects to the template1
database and executes the <command>CREATE DATABASE</> command,
exactly as described above. It uses <application>psql</> program
internally. The reference page on createdb contains the invocation
details. In particular, createdb without any arguments will create
a database with the current user name, which may or may not be what
you want.
</para>
<sect2>
<title>Alternative Locations</title>
<para>
Once you have constructed a database, you can access it
by:
It is possible to create a database in a location other than the
default. Remember that all database access occurs through the
database server backend, so that any location specified must be
accessible by the backend.
</para>
<itemizedlist spacing="compact" mark="bullet">
<listitem>
<para>
running the <productname>Postgres</productname> terminal monitor program
(<application>psql</application>) which allows you to interactively
enter, edit, and execute <acronym>SQL</acronym> commands.
</para>
</listitem>
<para>
Alternative database locations are referenced by an environment
variable which gives the absolute path to the intended storage
location. This environment variable must have been defined before
the backend was started. 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>
<listitem>
<para>
writing a C program using the <literal>libpq</literal> subroutine
library. This allows you to submit <acronym>SQL</acronym> commands
from C and get answers and status messages back to
your program. This interface is discussed further
in the <citetitle>PostgreSQL Programmer's Guide</citetitle>.
</para>
</listitem>
</itemizedlist>
<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
<xref linkend="postmaster-shutdown"> and <xref
linkend="postmaster-start">.) To set an environment variable, type
<informalexample>
<programlisting>
PGDATA2=/home/postgres/data
</programlisting>
</informalexample>
in Bourne shells, or
<informalexample>
<programlisting>
setenv PGDATA2 /home/postgres/data
</programlisting>
</informalexample>
in csh or 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 startup file or server
startup script.
</para>
You might want to start up <application>psql</application>,
to try out the examples in this manual. It can be activated for the
<replaceable class="parameter">dbname</replaceable> database by typing the command:
<para>
To create a data storage area in <envar>PGDATA2</>, ensure that
<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
<informalexample>
<programlisting>
initlocation PGDATA2
</programlisting>
</informalexample>
The you can restart the server.
</para>
<para>
To create a database at 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>
Database created at alternative locations using this method can be
accessed and dropped like any other database.
</para>
<note>
<para>
It can also be possible to specify absolute paths directly to the
<command>CREATE DATABASE</> command without defining environment
variables. This is disallowed by default because it is a security
risk. To allow it, you must compile <productname>Postgres</> with
the C preprocessor macro <literal>ALLOW_ABSOLUTE_DBPATHS</>
defined. One way to do this is to run the compilation step like
this: <userinput>gmake COPT=-DALLOW_ABSOLUTE_DBPATHS all</>.
</para>
</note>
</sect2>
</sect1>
<sect1>
<title>Accessing a Database</title>
<para>
Once you have constructed a database, you can access it by:
<itemizedlist spacing="compact" mark="bullet">
<listitem>
<para>
running the <productname>Postgres</productname> terminal monitor program
(<application>psql</application>) which allows you to interactively
enter, edit, and execute <acronym>SQL</acronym> commands.
</para>
</listitem>
<listitem>
<para>
writing a C program using the <literal>libpq</literal> subroutine
library. This allows you to submit <acronym>SQL</acronym> commands
from C and get answers and status messages back to
your program. This interface is discussed further
in the <citetitle>PostgreSQL Programmer's Guide</citetitle>.
</para>
</listitem>
</itemizedlist>
You might want to start up <application>psql</application>,
to try out the examples in this manual. It can be activated for the
<replaceable class="parameter">dbname</replaceable> database by typing the command:
<programlisting>
psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
You will be greeted with the following message:
You will be greeted with the following message:
<programlisting>
Welcome to psql, the PostgreSQL interactive terminal.
@ -138,151 +280,39 @@ Type: \copyright for distribution terms
are denoted by "<literal>/* ... */</literal>", a convention borrowed
from <productname>Ingres</productname>.
</para>
</sect1>
</sect1>
<sect1>
<title>Destroying a Database</title>
<sect1>
<title>Destroying a Database</title>
<para>
If you are the database administrator for the database
mydb, you can destroy it using the following Unix command:
<para>
Databases are destroyed with the command <command>DROP DATABASE</command>:
<synopsis>
DROP DATABASE <replaceable>name</>
</synopsis>
Only the owner of the database (i.e., the user that created it) can
drop databases. Dropping a databases removes all objects that were
contained within the database. The destruction of a database cannot
be undone.
</para>
<programlisting>
% dropdb <replaceable class="parameter">dbname</replaceable>
</programlisting>
<para>
You cannot execute the <command>DROP DATABASE</command> command
while connected to the victim database. You can, however, be
connected to any other database, including the template1 database,
which would be the only option for dropping the last database of a
given cluster.
</para>
This action physically removes all of the Unix files
associated with the database and cannot be undone, so
this should only be done with a great deal of forethought.
</para>
<para>
It is also possible to destroy a database from within an
<acronym>SQL</acronym> session by using
<programlisting>
&gt; drop database <replaceable class="parameter">dbname</replaceable>
</programlisting>
</para>
</sect1>
<sect1>
<title>Backup and Restore</title>
<caution>
<para>
Every database should be backed up on a regular basis. Since
<productname>Postgres</productname> manages it's own files in the
file system, it is <emphasis>not advisable</emphasis> to rely on
system backups of your file system for your database backups;
there is no guarantee that the files will be in a usable,
consistant state after restoration.
</para>
</caution>
<para>
<productname>Postgres</productname> provides two utilities to
backup your system: <application>pg_dump</application> to backup
individual databases and
<application>pg_dumpall</application> to backup your installation
in one step.
</para>
<para>
An individual database can be backed up using the following
command:
<programlisting>
% pg_dump <replaceable class="parameter">dbname</replaceable> &gt; <replaceable class="parameter">dbname</replaceable>.pgdump
</programlisting>
and can be restored using
<programlisting>
cat <replaceable class="parameter">dbname</replaceable>.pgdump | psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
</para>
<para>
This technique can be used to move databases to new
locations, and to rename existing databases.
</para>
<sect2>
<title>Large Databases</title>
<note>
<title>Author</title>
<para>
Written by <ulink url="hannu@trust.ee">Hannu Krosing</ulink> on
1999-06-19.
</para>
</note>
<para>
Since <productname>Postgres</productname> allows tables larger
than the maximum file size on your system, it can be problematic
to dump the table to a file, since the resulting file will likely
be larger than the maximum size allowed by your system.</para>
<para>
As <application>pg_dump</application> writes to stdout,
you can just use standard *nix tools
to work around this possible problem:
<itemizedlist>
<listitem>
<para>
Use compressed dumps:
<programlisting>
% pg_dump <replaceable class="parameter">dbname</replaceable> | gzip > <replaceable class="parameter">filename</replaceable>.dump.gz
</programlisting>
reload with
<programlisting>
% createdb <replaceable class="parameter">dbname</replaceable>
% gunzip -c <replaceable class="parameter">filename</replaceable>.dump.gz | psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
or
<programlisting>
% cat <replaceable class="parameter">filename</replaceable>.dump.gz | gunzip | psql <replaceable class="parameter">dbname</replaceable>
</programlisting>
</para>
</listitem>
<listitem>
<para>
Use split:
<programlisting>
% pg_dump <replaceable class="parameter">dbname</replaceable> | split -b 1m - <replaceable class="parameter">filename</replaceable>.dump.
</programlisting>
reload with
<programlisting>
% createdb <replaceable class="parameter">dbname</replaceable>
% cat <replaceable class="parameter">filename</replaceable>.dump.* | pgsql <replaceable class="parameter">dbname</replaceable>
</programlisting>
</para>
</listitem>
</itemizedlist>
</para>
<para>
Of course, the name of the file
(<replaceable class="parameter">filename</replaceable>) and the
content of the <application>pg_dump</application> output need not
match the name of the database. Also, the restored database can
have an arbitrary new name, so this mechanism is also suitable
for renaming databases.
</para>
</sect2>
</sect1>
<para>
For convenience, there is also a shell program to drop databases:
<synopsis>
dropdb <replaceable class="parameter">dbname</replaceable>
</synopsis>
(Unlike <command>createdb</>, it is not the default action to drop
the database with the current user name.)
</para>
</sect1>
</chapter>
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@ -1,123 +0,0 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/Attic/start-ag.sgml,v 1.11 2000/06/18 21:24:51 petere Exp $
- This file currently contains several small chapters.
- Each chapter should be split off into a separate source file...
- - thomas 1998-02-24
-->
<chapter id="disk">
<title>Disk Management</title>
<sect1>
<title>Alternate Locations</title>
<para>
It is possible to create a database in a location other than the default
location for the installation. Remember that all database access actually
occurs through the database backend, so that any location specified must
be accessible by the backend.
</para>
<para>
Alternate database locations are created and referenced by an environment variable
which gives the absolute path to the intended storage location.
This environment variable must have been defined before the backend was started
and must be writable by the postgres administrator account.
Any valid environment variable name may be used to reference an alternate
location, although using variable name with a prefix of PGDATA is recommended
to avoid confusion and conflict with other variables.
</para>
<note>
<para>
In previous versions of <productname>Postgres</productname>,
it was also permissable to use an absolute path name
to specify an alternate storage location.
The environment variable style of specification
is to be preferred since it allows the site administrator more flexibility in
managing disk storage.
If you prefer using absolute paths, you may do so by defining
"ALLOW_ABSOLUTE_DBPATHS" and recompiling <productname>Postgres</productname>
To do this, either add this line
<programlisting>
#define ALLOW_ABSOLUTE_DBPATHS 1
</programlisting>
to the file <filename>src/include/config.h</filename>, or by specifying
<programlisting>
CFLAGS+= -DALLOW_ABSOLUTE_DBPATHS
</programlisting>
in your <filename>Makefile.custom</filename>.
</para>
</note>
<para>
Remember that database creation is actually performed by the database backend.
Therefore, any environment variable specifying an alternate location must have
been defined before the backend was started. To define an alternate location
PGDATA2 pointing to <filename>/home/postgres/data</filename>, first type
<programlisting>
% setenv PGDATA2 /home/postgres/data
</programlisting>
to define the environment variable to be used with subsequent commands.
Usually, you will want to define this variable in the
<productname>Postgres</productname> superuser's
<filename>.profile</filename>
or
<filename>.cshrc</filename>
initialization file to ensure that it is defined upon system startup.
Any environment variable can be used to reference alternate location,
although it is preferred that the variables be prefixed with "PGDATA"
to eliminate confusion and the possibility of conflicting with or
overwriting other variables.
</para>
<para>
To create a data storage area in PGDATA2, ensure
that <filename>/home/postgres</filename> already exists and is writable
by the postgres administrator.
Then from the command line, type
<programlisting>
% setenv PGDATA2 /home/postgres/data
% initlocation $PGDATA2
Creating Postgres database system directory /home/postgres/data
Creating Postgres database system directory /home/postgres/data/base
</programlisting>
</para>
<para>
To test the new location, create a database <database>test</database> by typing
<programlisting>
% createdb -D PGDATA2 test
% dropdb test
</programlisting>
</para>
</sect1>
</chapter>
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Local variables:
mode:sgml
sgml-omittag:nil
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"./reference.ced"
sgml-exposed-tags:nil
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sgml-local-ecat-files:nil
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@ -56,7 +56,7 @@ CREATE USER <replaceable>name</replaceable>
constrained in its login name by her real name.)
</para>
<sect2>
<sect2 id="user-attributes">
<title>User attributes</title>
<para>