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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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>pg_receivewal</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="app-pg-isready.html" title="pg_isready" /><link rel="next" href="app-pgrecvlogical.html" title="pg_recvlogical" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center"><span class="application">pg_receivewal</span></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="app-pg-isready.html" title="pg_isready">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="reference-client.html" title="PostgreSQL Client Applications">Up</a></td><th width="60%" align="center">PostgreSQL Client Applications</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="app-pgrecvlogical.html" title="pg_recvlogical">Next</a></td></tr></table><hr /></div><div class="refentry" id="APP-PGRECEIVEWAL"><div class="titlepage"></div><a id="id-1.9.4.16.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle"><span class="application">pg_receivewal</span></span></h2><p>pg_receivewal — stream write-ahead logs from a <span class="productname">PostgreSQL</span> server</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="cmdsynopsis"><p id="id-1.9.4.16.4.1"><code class="command">pg_receivewal</code> [<em class="replaceable"><code>option</code></em>...]</p></div></div><div class="refsect1" id="id-1.9.4.16.5"><h2>Description</h2><p>
<span class="application">pg_receivewal</span> is used to stream the write-ahead log
from a running <span class="productname">PostgreSQL</span> cluster. The write-ahead
log is streamed using the streaming replication protocol, and is written
to a local directory of files. This directory can be used as the archive
location for doing a restore using point-in-time recovery (see
<a class="xref" href="continuous-archiving.html" title="26.3. Continuous Archiving and Point-in-Time Recovery (PITR)">Section 26.3</a>).
</p><p>
<span class="application">pg_receivewal</span> streams the write-ahead
log in real time as it's being generated on the server, and does not wait
for segments to complete like <a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-COMMAND">archive_command</a> and
<a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-LIBRARY">archive_library</a> do.
For this reason, it is not necessary to set
<a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-TIMEOUT">archive_timeout</a> when using
<span class="application">pg_receivewal</span>.
</p><p>
Unlike the WAL receiver of a PostgreSQL standby server, <span class="application">pg_receivewal</span>
by default flushes WAL data only when a WAL file is closed.
The option <code class="option">--synchronous</code> must be specified to flush WAL data
in real time. Since <span class="application">pg_receivewal</span> does not
apply WAL, you should not allow it to become a synchronous standby when
<a class="xref" href="runtime-config-wal.html#GUC-SYNCHRONOUS-COMMIT">synchronous_commit</a> equals
<code class="literal">remote_apply</code>. If it does, it will appear to be a
standby that never catches up, and will cause transaction commits to
block. To avoid this, you should either configure an appropriate value
for <a class="xref" href="runtime-config-replication.html#GUC-SYNCHRONOUS-STANDBY-NAMES">synchronous_standby_names</a>, or specify
<code class="varname">application_name</code> for
<span class="application">pg_receivewal</span> that does not match it, or
change the value of <code class="varname">synchronous_commit</code> to
something other than <code class="literal">remote_apply</code>.
</p><p>
The write-ahead log is streamed over a regular
<span class="productname">PostgreSQL</span> connection and uses the replication
protocol. The connection must be made with a user having
<code class="literal">REPLICATION</code> permissions (see
<a class="xref" href="role-attributes.html" title="22.2. Role Attributes">Section 22.2</a>) or a superuser, and
<code class="filename">pg_hba.conf</code> must permit the replication connection.
The server must also be configured with
<a class="xref" href="runtime-config-replication.html#GUC-MAX-WAL-SENDERS">max_wal_senders</a> set high enough to leave at least
one session available for the stream.
</p><p>
The starting point of the write-ahead log streaming is calculated when
<span class="application">pg_receivewal</span> starts:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
First, scan the directory where the WAL segment files are written and
find the newest completed segment file, using as the starting point the
beginning of the next WAL segment file.
</p></li><li class="listitem"><p>
If a starting point cannot be calculated with the previous method,
and if a replication slot is used, an extra
<code class="command">READ_REPLICATION_SLOT</code> command is issued to retrieve
the slot's <code class="literal">restart_lsn</code> to use as the starting point.
This option is only available when streaming write-ahead logs from
<span class="productname">PostgreSQL</span> 15 and up.
</p></li><li class="listitem"><p>
If a starting point cannot be calculated with the previous method,
the latest WAL flush location is used as reported by the server from
an <code class="literal">IDENTIFY_SYSTEM</code> command.
</p></li></ol></div><p>
</p><p>
If the connection is lost, or if it cannot be initially established,
with a non-fatal error, <span class="application">pg_receivewal</span> will
retry the connection indefinitely, and reestablish streaming as soon
as possible. To avoid this behavior, use the <code class="literal">-n</code>
parameter.
</p><p>
In the absence of fatal errors, <span class="application">pg_receivewal</span>
will run until terminated by the <span class="systemitem">SIGINT</span> signal
(<span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>C</strong></span>).
</p></div><div class="refsect1" id="id-1.9.4.16.6"><h2>Options</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-D <em class="replaceable"><code>directory</code></em></code><br /></span><span class="term"><code class="option">--directory=<em class="replaceable"><code>directory</code></em></code></span></dt><dd><p>
Directory to write the output to.
</p><p>
This parameter is required.
</p></dd><dt><span class="term"><code class="option">-E <em class="replaceable"><code>lsn</code></em></code><br /></span><span class="term"><code class="option">--endpos=<em class="replaceable"><code>lsn</code></em></code></span></dt><dd><p>
Automatically stop replication and exit with normal exit status 0 when
receiving reaches the specified LSN.
</p><p>
If there is a record with LSN exactly equal to <em class="replaceable"><code>lsn</code></em>,
the record will be processed.
</p></dd><dt><span class="term"><code class="option">--if-not-exists</code></span></dt><dd><p>
Do not error out when <code class="option">--create-slot</code> is specified
and a slot with the specified name already exists.
</p></dd><dt><span class="term"><code class="option">-n</code><br /></span><span class="term"><code class="option">--no-loop</code></span></dt><dd><p>
Don't loop on connection errors. Instead, exit right away with
an error.
</p></dd><dt><span class="term"><code class="option">--no-sync</code></span></dt><dd><p>
This option causes <code class="command">pg_receivewal</code> to not force WAL
data to be flushed to disk. This is faster, but means that a
subsequent operating system crash can leave the WAL segments corrupt.
Generally, this option is useful for testing but should not be used
when doing WAL archiving on a production deployment.
</p><p>
This option is incompatible with <code class="literal">--synchronous</code>.
</p></dd><dt><span class="term"><code class="option">-s <em class="replaceable"><code>interval</code></em></code><br /></span><span class="term"><code class="option">--status-interval=<em class="replaceable"><code>interval</code></em></code></span></dt><dd><p>
Specifies the number of seconds between status packets sent back to the
server. This allows for easier monitoring of the progress from server.
A value of zero disables the periodic status updates completely,
although an update will still be sent when requested by the server, to
avoid timeout disconnect. The default value is 10 seconds.
</p></dd><dt><span class="term"><code class="option">-S <em class="replaceable"><code>slotname</code></em></code><br /></span><span class="term"><code class="option">--slot=<em class="replaceable"><code>slotname</code></em></code></span></dt><dd><p>
Require <span class="application">pg_receivewal</span> to use an existing
replication slot (see <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="27.2.6. Replication Slots">Section 27.2.6</a>).
When this option is used, <span class="application">pg_receivewal</span> will report
a flush position to the server, indicating when each segment has been
synchronized to disk so that the server can remove that segment if it
is not otherwise needed.
</p><p>
When the replication client
of <span class="application">pg_receivewal</span> is configured on the
server as a synchronous standby, then using a replication slot will
report the flush position to the server, but only when a WAL file is
closed. Therefore, that configuration will cause transactions on the
primary to wait for a long time and effectively not work
satisfactorily. The option <code class="literal">--synchronous</code> (see
below) must be specified in addition to make this work correctly.
</p></dd><dt><span class="term"><code class="option">--synchronous</code></span></dt><dd><p>
Flush the WAL data to disk immediately after it has been received. Also
send a status packet back to the server immediately after flushing,
regardless of <code class="literal">--status-interval</code>.
</p><p>
This option should be specified if the replication client
of <span class="application">pg_receivewal</span> is configured on the
server as a synchronous standby, to ensure that timely feedback is
sent to the server.
</p></dd><dt><span class="term"><code class="option">-v</code><br /></span><span class="term"><code class="option">--verbose</code></span></dt><dd><p>
Enables verbose mode.
</p></dd><dt><span class="term"><code class="option">-Z <em class="replaceable"><code>level</code></em></code><br /></span><span class="term"><code class="option">-Z <em class="replaceable"><code>method</code></em>[:<em class="replaceable"><code>detail</code></em>]</code><br /></span><span class="term"><code class="option">--compress=<em class="replaceable"><code>level</code></em></code><br /></span><span class="term"><code class="option">--compress=<em class="replaceable"><code>method</code></em>[:<em class="replaceable"><code>detail</code></em>]</code></span></dt><dd><p>
Enables compression of write-ahead logs.
</p><p>
The compression method can be set to <code class="literal">gzip</code>,
<code class="literal">lz4</code> (if <span class="productname">PostgreSQL</span>
was compiled with <code class="option">--with-lz4</code>) or
<code class="literal">none</code> for no compression.
A compression detail string can optionally be specified. If the
detail string is an integer, it specifies the compression level.
Otherwise, it should be a comma-separated list of items, each of the
form <code class="literal">keyword</code> or <code class="literal">keyword=value</code>.
Currently, the only supported keyword is <code class="literal">level</code>.
</p><p>
If no compression level is specified, the default compression level
will be used. If only a level is specified without mentioning an
algorithm, <code class="literal">gzip</code> compression will be used if the
level is greater than 0, and no compression will be used if the level
is 0.
</p><p>
The suffix <code class="filename">.gz</code> will automatically be added to
all filenames when using <code class="literal">gzip</code>, and the suffix
<code class="filename">.lz4</code> is added when using <code class="literal">lz4</code>.
</p></dd></dl></div><p>
The following command-line options control the database connection parameters.
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-d <em class="replaceable"><code>connstr</code></em></code><br /></span><span class="term"><code class="option">--dbname=<em class="replaceable"><code>connstr</code></em></code></span></dt><dd><p>
Specifies parameters used to connect to the server, as a <a class="link" href="libpq-connect.html#LIBPQ-CONNSTRING" title="34.1.1. Connection Strings">connection string</a>; these
will override any conflicting command line options.
</p><p>
The option is called <code class="literal">--dbname</code> for consistency with other
client applications, but because <span class="application">pg_receivewal</span>
doesn't connect to any particular database in the cluster, database
name in the connection string will be ignored.
</p></dd><dt><span class="term"><code class="option">-h <em class="replaceable"><code>host</code></em></code><br /></span><span class="term"><code class="option">--host=<em class="replaceable"><code>host</code></em></code></span></dt><dd><p>
Specifies the host name of the machine on which the server is
running. If the value begins with a slash, it is used as the
directory for the Unix domain socket. The default is taken
from the <code class="envar">PGHOST</code> environment variable, if set,
else a Unix domain socket connection is attempted.
</p></dd><dt><span class="term"><code class="option">-p <em class="replaceable"><code>port</code></em></code><br /></span><span class="term"><code class="option">--port=<em class="replaceable"><code>port</code></em></code></span></dt><dd><p>
Specifies the TCP port or local Unix domain socket file
extension on which the server is listening for connections.
Defaults to the <code class="envar">PGPORT</code> environment variable, if
set, or a compiled-in default.
</p></dd><dt><span class="term"><code class="option">-U <em class="replaceable"><code>username</code></em></code><br /></span><span class="term"><code class="option">--username=<em class="replaceable"><code>username</code></em></code></span></dt><dd><p>
User name to connect as.
</p></dd><dt><span class="term"><code class="option">-w</code><br /></span><span class="term"><code class="option">--no-password</code></span></dt><dd><p>
Never issue a password prompt. If the server requires
password authentication and a password is not available by
other means such as a <code class="filename">.pgpass</code> file, the
connection attempt will fail. This option can be useful in
batch jobs and scripts where no user is present to enter a
password.
</p></dd><dt><span class="term"><code class="option">-W</code><br /></span><span class="term"><code class="option">--password</code></span></dt><dd><p>
Force <span class="application">pg_receivewal</span> to prompt for a
password before connecting to a database.
</p><p>
This option is never essential, since
<span class="application">pg_receivewal</span> will automatically prompt
for a password if the server demands password authentication.
However, <span class="application">pg_receivewal</span> will waste a
connection attempt finding out that the server wants a password.
In some cases it is worth typing <code class="option">-W</code> to avoid the extra
connection attempt.
</p></dd></dl></div><p>
</p><p>
<span class="application">pg_receivewal</span> can perform one of the two
following actions in order to control physical replication slots:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">--create-slot</code></span></dt><dd><p>
Create a new physical replication slot with the name specified in
<code class="option">--slot</code>, then exit.
</p></dd><dt><span class="term"><code class="option">--drop-slot</code></span></dt><dd><p>
Drop the replication slot with the name specified in
<code class="option">--slot</code>, then exit.
</p></dd></dl></div><p>
</p><p>
Other options are also available:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-V</code><br /></span><span class="term"><code class="option">--version</code></span></dt><dd><p>
Print the <span class="application">pg_receivewal</span> version and exit.
</p></dd><dt><span class="term"><code class="option">-?</code><br /></span><span class="term"><code class="option">--help</code></span></dt><dd><p>
Show help about <span class="application">pg_receivewal</span> command line
arguments, and exit.
</p></dd></dl></div><p>
</p></div><div class="refsect1" id="id-1.9.4.16.7"><h2>Exit Status</h2><p>
<span class="application">pg_receivewal</span> will exit with status 0 when
terminated by the <span class="systemitem">SIGINT</span> signal. (That is the
normal way to end it. Hence it is not an error.) For fatal errors or
other signals, the exit status will be nonzero.
</p></div><div class="refsect1" id="id-1.9.4.16.8"><h2>Environment</h2><p>
This utility, like most other <span class="productname">PostgreSQL</span> utilities,
uses the environment variables supported by <span class="application">libpq</span>
(see <a class="xref" href="libpq-envars.html" title="34.15. Environment Variables">Section 34.15</a>).
</p><p>
The environment variable <code class="envar">PG_COLOR</code> specifies whether to use
color in diagnostic messages. Possible values are
<code class="literal">always</code>, <code class="literal">auto</code> and
<code class="literal">never</code>.
</p></div><div class="refsect1" id="id-1.9.4.16.9"><h2>Notes</h2><p>
When using <span class="application">pg_receivewal</span> instead of
<a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-COMMAND">archive_command</a> or
<a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-LIBRARY">archive_library</a> as the main WAL backup method, it is
strongly recommended to use replication slots. Otherwise, the server is
free to recycle or remove write-ahead log files before they are backed up,
because it does not have any information, either
from <a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-COMMAND">archive_command</a> or
<a class="xref" href="runtime-config-wal.html#GUC-ARCHIVE-LIBRARY">archive_library</a> or the replication slots, about
how far the WAL stream has been archived. Note, however, that a
replication slot will fill up the server's disk space if the receiver does
not keep up with fetching the WAL data.
</p><p>
<span class="application">pg_receivewal</span> will preserve group permissions on
the received WAL files if group permissions are enabled on the source
cluster.
</p></div><div class="refsect1" id="id-1.9.4.16.10"><h2>Examples</h2><p>
To stream the write-ahead log from the server at
<code class="literal">mydbserver</code> and store it in the local directory
<code class="filename">/usr/local/pgsql/archive</code>:
</p><pre class="screen">
<code class="prompt">$</code> <strong class="userinput"><code>pg_receivewal -h mydbserver -D /usr/local/pgsql/archive</code></strong>
</pre></div><div class="refsect1" id="id-1.9.4.16.11"><h2>See Also</h2><span class="simplelist"><a class="xref" href="app-pgbasebackup.html" title="pg_basebackup"><span class="refentrytitle"><span class="application">pg_basebackup</span></span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="app-pg-isready.html" title="pg_isready">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="reference-client.html" title="PostgreSQL Client Applications">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="app-pgrecvlogical.html" title="pg_recvlogical">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span class="application">pg_isready</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="40%" align="right" valign="top"> <span class="application">pg_recvlogical</span></td></tr></table></div></body></html>
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