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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>25.1. SQL Dump</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="backup.html" title="Chapter 25. Backup and Restore" /><link rel="next" href="backup-file.html" title="25.2. File System Level Backup" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">25.1. <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym> Dump</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="backup.html" title="Chapter 25. Backup and Restore">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="backup.html" title="Chapter 25. Backup and Restore">Up</a></td><th width="60%" align="center">Chapter 25. Backup and Restore</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="backup-file.html" title="25.2. File System Level Backup">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="BACKUP-DUMP"><div class="titlepage"><div><div><h2 class="title" style="clear: both">25.1. <acronym class="acronym">SQL</acronym> Dump</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="backup-dump.html#BACKUP-DUMP-RESTORE">25.1.1. Restoring the Dump</a></span></dt><dt><span class="sect2"><a href="backup-dump.html#BACKUP-DUMP-ALL">25.1.2. Using <span class="application">pg_dumpall</span></a></span></dt><dt><span class="sect2"><a href="backup-dump.html#BACKUP-DUMP-LARGE">25.1.3. Handling Large Databases</a></span></dt></dl></div><p>
The idea behind this dump method is to generate a 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.
<span class="productname">PostgreSQL</span> provides the utility program
<a class="xref" href="app-pgdump.html" title="pg_dump"><span class="refentrytitle">pg_dump</span></a> for this purpose. The basic usage of this
command is:
</p><pre class="synopsis">
pg_dump <em class="replaceable"><code>dbname</code></em> > <em class="replaceable"><code>dumpfile</code></em>
</pre><p>
As you see, <span class="application">pg_dump</span> writes its result to the
standard output. We will see below how this can be useful.
While the above command creates a text file, <span class="application">pg_dump</span>
can create files in other formats that allow for parallelism and more
fine-grained control of object restoration.
</p><p>
<span class="application">pg_dump</span> is a regular <span class="productname">PostgreSQL</span>
client application (albeit a particularly clever one). This means
that you can perform this backup procedure from any remote host that has
access to the database. But remember that <span class="application">pg_dump</span>
does not operate with special permissions. In particular, it must
have read access to all tables that you want to back up, so in order
to back up the entire database you almost always have to run it as a
database superuser. (If you do not have sufficient privileges to back up
the entire database, you can still back up portions of the database to which
you do have access using options such as
<code class="option">-n <em class="replaceable"><code>schema</code></em></code>
or <code class="option">-t <em class="replaceable"><code>table</code></em></code>.)
</p><p>
To specify which database server <span class="application">pg_dump</span> should
contact, use the command line options <code class="option">-h
<em class="replaceable"><code>host</code></em></code> and <code class="option">-p <em class="replaceable"><code>port</code></em></code>. The
default host is the local host or whatever your
<code class="envar">PGHOST</code> environment variable specifies. Similarly,
the default port is indicated by the <code class="envar">PGPORT</code>
environment variable or, failing that, by the compiled-in default.
(Conveniently, the server will normally have the same compiled-in
default.)
</p><p>
Like any other <span class="productname">PostgreSQL</span> client application,
<span class="application">pg_dump</span> will by default connect with the database
user name that is equal to the current operating system user name. To override
this, either specify the <code class="option">-U</code> option or set the
environment variable <code class="envar">PGUSER</code>. Remember that
<span class="application">pg_dump</span> connections are subject to the normal
client authentication mechanisms (which are described in <a class="xref" href="client-authentication.html" title="Chapter 20. Client Authentication">Chapter 20</a>).
</p><p>
An important advantage of <span class="application">pg_dump</span> over the other backup
methods described later is that <span class="application">pg_dump</span>'s output can
generally be re-loaded into newer versions of <span class="productname">PostgreSQL</span>,
whereas file-level backups and continuous archiving are both extremely
server-version-specific. <span class="application">pg_dump</span> is also the only method
that will work when transferring a database to a different machine
architecture, such as going from a 32-bit to a 64-bit server.
</p><p>
Dumps created by <span class="application">pg_dump</span> are internally consistent,
meaning, the dump represents a snapshot of the database at the time
<span class="application">pg_dump</span> began running. <span class="application">pg_dump</span> 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 most forms of <code class="command">ALTER TABLE</code>.)
</p><div class="sect2" id="BACKUP-DUMP-RESTORE"><div class="titlepage"><div><div><h3 class="title">25.1.1. Restoring the Dump</h3></div></div></div><p>
Text files created by <span class="application">pg_dump</span> are intended to
be read in by the <span class="application">psql</span> program. The
general command form to restore a dump is
</p><pre class="synopsis">
psql <em class="replaceable"><code>dbname</code></em> < <em class="replaceable"><code>dumpfile</code></em>
</pre><p>
where <em class="replaceable"><code>dumpfile</code></em> is the
file output by the <span class="application">pg_dump</span> command. The database <em class="replaceable"><code>dbname</code></em> will not be created by this
command, so you must create it yourself from <code class="literal">template0</code>
before executing <span class="application">psql</span> (e.g., with
<code class="literal">createdb -T template0 <em class="replaceable"><code>dbname</code></em></code>). <span class="application">psql</span>
supports options similar to <span class="application">pg_dump</span> for specifying
the database server to connect to and the user name to use. See
the <a class="xref" href="app-psql.html" title="psql"><span class="refentrytitle"><span class="application">psql</span></span></a> reference page for more information.
Non-text file dumps are restored using the <a class="xref" href="app-pgrestore.html" title="pg_restore"><span class="refentrytitle">pg_restore</span></a> utility.
</p><p>
Before restoring an SQL dump, all the users who own objects or were
granted permissions on objects in the dumped database must already
exist. If they do not, the restore will fail to recreate the
objects with the original ownership and/or permissions.
(Sometimes this is what you want, but usually it is not.)
</p><p>
By default, the <span class="application">psql</span> script will continue to
execute after an SQL error is encountered. You might wish to run
<span class="application">psql</span> with
the <code class="literal">ON_ERROR_STOP</code> variable set to alter that
behavior and have <span class="application">psql</span> exit with an
exit status of 3 if an SQL error occurs:
</p><pre class="programlisting">
psql --set ON_ERROR_STOP=on <em class="replaceable"><code>dbname</code></em> < <em class="replaceable"><code>dumpfile</code></em>
</pre><p>
Either way, you will only have a partially restored database.
Alternatively, you can specify that the whole dump should be
restored as a single transaction, so the restore is either fully
completed or fully rolled back. This mode can be specified by
passing the <code class="option">-1</code> or <code class="option">--single-transaction</code>
command-line options to <span class="application">psql</span>. When using this
mode, be aware that even a minor error can rollback a
restore that has already run for many hours. However, that might
still be preferable to manually cleaning up a complex database
after a partially restored dump.
</p><p>
The ability of <span class="application">pg_dump</span> and <span class="application">psql</span> to
write to or read from pipes makes it possible to dump a database
directly from one server to another, for example:
</p><pre class="programlisting">
pg_dump -h <em class="replaceable"><code>host1</code></em> <em class="replaceable"><code>dbname</code></em> | psql -h <em class="replaceable"><code>host2</code></em> <em class="replaceable"><code>dbname</code></em>
</pre><p>
</p><div class="important"><h3 class="title">Important</h3><p>
The dumps produced by <span class="application">pg_dump</span> are relative to
<code class="literal">template0</code>. This means that any languages, procedures,
etc. added via <code class="literal">template1</code> will also be dumped by
<span class="application">pg_dump</span>. As a result, when restoring, if you are
using a customized <code class="literal">template1</code>, you must create the
empty database from <code class="literal">template0</code>, as in the example
above.
</p></div><p>
After restoring a backup, it is wise to run <a class="xref" href="sql-analyze.html" title="ANALYZE"><span class="refentrytitle">ANALYZE</span></a> on each
database so the query optimizer has useful statistics;
see <a class="xref" href="routine-vacuuming.html#VACUUM-FOR-STATISTICS" title="24.1.3. Updating Planner Statistics">Section 24.1.3</a>
and <a class="xref" href="routine-vacuuming.html#AUTOVACUUM" title="24.1.6. The Autovacuum Daemon">Section 24.1.6</a> for more information.
For more advice on how to load large amounts of data
into <span class="productname">PostgreSQL</span> efficiently, refer to <a class="xref" href="populate.html" title="14.4. Populating a Database">Section 14.4</a>.
</p></div><div class="sect2" id="BACKUP-DUMP-ALL"><div class="titlepage"><div><div><h3 class="title">25.1.2. Using <span class="application">pg_dumpall</span></h3></div></div></div><p>
<span class="application">pg_dump</span> dumps only a single database at a time,
and it does not dump information about roles or tablespaces
(because those are cluster-wide rather than per-database).
To support convenient dumping of the entire contents of a database
cluster, the <a class="xref" href="app-pg-dumpall.html" title="pg_dumpall"><span class="refentrytitle"><span class="application">pg_dumpall</span></span></a> program is provided.
<span class="application">pg_dumpall</span> backs up each database in a given
cluster, and also preserves cluster-wide data such as role and
tablespace definitions. The basic usage of this command is:
</p><pre class="synopsis">
pg_dumpall > <em class="replaceable"><code>dumpfile</code></em>
</pre><p>
The resulting dump can be restored with <span class="application">psql</span>:
</p><pre class="synopsis">
psql -f <em class="replaceable"><code>dumpfile</code></em> postgres
</pre><p>
(Actually, you can specify any existing database name to start from,
but if you are loading into an empty cluster then <code class="literal">postgres</code>
should usually be used.) It is always necessary to have
database superuser access when restoring a <span class="application">pg_dumpall</span>
dump, as that is required to restore the role and tablespace information.
If you use tablespaces, make sure that the tablespace paths in the
dump are appropriate for the new installation.
</p><p>
<span class="application">pg_dumpall</span> works by emitting commands to re-create
roles, tablespaces, and empty databases, then invoking
<span class="application">pg_dump</span> for each database. This means that while
each database will be internally consistent, the snapshots of
different databases are not synchronized.
</p><p>
Cluster-wide data can be dumped alone using the
<span class="application">pg_dumpall</span> <code class="option">--globals-only</code> option.
This is necessary to fully backup the cluster if running the
<span class="application">pg_dump</span> command on individual databases.
</p></div><div class="sect2" id="BACKUP-DUMP-LARGE"><div class="titlepage"><div><div><h3 class="title">25.1.3. Handling Large Databases</h3></div></div></div><p>
Some operating systems have maximum file size limits that cause
problems when creating large <span class="application">pg_dump</span> output files.
Fortunately, <span class="application">pg_dump</span> can write to the standard
output, so you can use standard Unix tools to work around this
potential problem. There are several possible methods:
</p><p><strong>Use compressed dumps. </strong>
You can use your favorite compression program, for example
<span class="application">gzip</span>:
</p><pre class="programlisting">
pg_dump <em class="replaceable"><code>dbname</code></em> | gzip > <em class="replaceable"><code>filename</code></em>.gz
</pre><p>
Reload with:
</p><pre class="programlisting">
gunzip -c <em class="replaceable"><code>filename</code></em>.gz | psql <em class="replaceable"><code>dbname</code></em>
</pre><p>
or:
</p><pre class="programlisting">
cat <em class="replaceable"><code>filename</code></em>.gz | gunzip | psql <em class="replaceable"><code>dbname</code></em>
</pre><p>
</p><p><strong>Use <code class="command">split</code>. </strong>
The <code class="command">split</code> command
allows you to split the output into smaller files that are
acceptable in size to the underlying file system. For example, to
make chunks of 1 megabyte:
</p><pre class="programlisting">
pg_dump <em class="replaceable"><code>dbname</code></em> | split -b 1m - <em class="replaceable"><code>filename</code></em>
</pre><p>
Reload with:
</p><pre class="programlisting">
cat <em class="replaceable"><code>filename</code></em>* | psql <em class="replaceable"><code>dbname</code></em>
</pre><p>
</p><p><strong>Use <span class="application">pg_dump</span>'s custom dump format. </strong>
If <span class="productname">PostgreSQL</span> was built on a system with the
<span class="application">zlib</span> compression library installed, the custom dump
format will compress data as it writes it to the output file. This will
produce dump file sizes similar to using <code class="command">gzip</code>, but it
has the added advantage that tables can be restored selectively. The
following command dumps a database using the custom dump format:
</p><pre class="programlisting">
pg_dump -Fc <em class="replaceable"><code>dbname</code></em> > <em class="replaceable"><code>filename</code></em>
</pre><p>
A custom-format dump is not a script for <span class="application">psql</span>, but
instead must be restored with <span class="application">pg_restore</span>, for example:
</p><pre class="programlisting">
pg_restore -d <em class="replaceable"><code>dbname</code></em> <em class="replaceable"><code>filename</code></em>
</pre><p>
See the <a class="xref" href="app-pgdump.html" title="pg_dump"><span class="refentrytitle">pg_dump</span></a> and <a class="xref" href="app-pgrestore.html" title="pg_restore"><span class="refentrytitle">pg_restore</span></a> reference pages for details.
</p><p>
For very large databases, you might need to combine <code class="command">split</code>
with one of the other two approaches.
</p><p><strong>Use <span class="application">pg_dump</span>'s parallel dump feature. </strong>
To speed up the dump of a large database, you can use
<span class="application">pg_dump</span>'s parallel mode. This will dump
multiple tables at the same time. You can control the degree of
parallelism with the <code class="command">-j</code> parameter. Parallel dumps
are only supported for the "directory" archive format.
</p><pre class="programlisting">
pg_dump -j <em class="replaceable"><code>num</code></em> -F d -f <em class="replaceable"><code>out.dir</code></em> <em class="replaceable"><code>dbname</code></em>
</pre><p>
You can use <code class="command">pg_restore -j</code> to restore a dump in parallel.
This will work for any archive of either the "custom" or the "directory"
archive mode, whether or not it has been created with <code class="command">pg_dump -j</code>.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="backup.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="backup.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="backup-file.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 25. Backup and Restore </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 25.2. File System Level Backup</td></tr></table></div></body></html>
