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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>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 16.3 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> |
| (<span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>C</strong></span>) |
| or <span class="systemitem">SIGTERM</span> signal. |
| </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> or |
| <span class="systemitem">SIGTERM</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 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> <span class="application">pg_recvlogical</span></td></tr></table></div></body></html> |
