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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_resetwal</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-ctl.html" title="pg_ctl" /><link rel="next" href="app-pgrewind.html" title="pg_rewind" /></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_resetwal</span></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="app-pg-ctl.html" title="pg_ctl">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="reference-server.html" title="PostgreSQL Server Applications">Up</a></td><th width="60%" align="center">PostgreSQL Server Applications</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="app-pgrewind.html" title="pg_rewind">Next</a></td></tr></table><hr /></div><div class="refentry" id="APP-PGRESETWAL"><div class="titlepage"></div><a id="id-1.9.5.8.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle"><span class="application">pg_resetwal</span></span></h2><p>pg_resetwal — reset the write-ahead log and other control information of a <span class="productname">PostgreSQL</span> database cluster</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="cmdsynopsis"><p id="id-1.9.5.8.4.1"><code class="command">pg_resetwal</code> [ <code class="option">-f</code>  |   <code class="option">--force</code> ] [ <code class="option">-n</code>  |   <code class="option">--dry-run</code> ] [<em class="replaceable"><code>option</code></em>...]  [ <code class="option">-D</code>  |   <code class="option">--pgdata</code> ]<em class="replaceable"><code>datadir</code></em> </p></div></div><div class="refsect1" id="R1-APP-PGRESETWAL-1"><h2>Description</h2><p>
   <code class="command">pg_resetwal</code> clears the write-ahead log (WAL) and
   optionally resets some other control information stored in the
   <code class="filename">pg_control</code> file.  This function is sometimes needed
   if these files have become corrupted.  It should be used only as a
   last resort, when the server will not start due to such corruption.
  </p><p>
   After running this command, it should be possible to start the server,
   but bear in mind that the database might contain inconsistent data due to
   partially-committed transactions.  You should immediately dump your data,
   run <code class="command">initdb</code>, and restore.  After restore, check for
   inconsistencies and repair as needed.
  </p><p>
   This utility can only be run by the user who installed the server, because
   it requires read/write access to the data directory.
   For safety reasons, you must specify the data directory on the command line.
   <code class="command">pg_resetwal</code> does not use the environment variable
   <code class="envar">PGDATA</code>.
  </p><p>
   If <code class="command">pg_resetwal</code> complains that it cannot determine
   valid data for <code class="filename">pg_control</code>, you can force it to proceed anyway
   by specifying the <code class="option">-f</code> (force) option.  In this case plausible
   values will be substituted for the missing data.  Most of the fields can be
   expected to match, but manual assistance might be needed for the next OID,
   next transaction ID and epoch, next multitransaction ID and offset, and
   WAL starting location fields. These fields can be set using the options
   discussed below. If you are not able to determine correct values for all
   these fields, <code class="option">-f</code> can still be used, but
   the recovered database must be treated with even more suspicion than
   usual: an immediate dump and restore is imperative.  <span class="emphasis"><em>Do not</em></span>
   execute any data-modifying operations in the database before you dump,
   as any such action is likely to make the corruption worse.
  </p></div><div class="refsect1" id="id-1.9.5.8.6"><h2>Options</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-f</code><br /></span><span class="term"><code class="option">--force</code></span></dt><dd><p>
      Force <code class="command">pg_resetwal</code> to proceed even if it cannot determine
      valid data for <code class="filename">pg_control</code>, as explained above.
     </p></dd><dt><span class="term"><code class="option">-n</code><br /></span><span class="term"><code class="option">--dry-run</code></span></dt><dd><p>
      The <code class="option">-n</code>/<code class="option">--dry-run</code> option instructs
      <code class="command">pg_resetwal</code> to print the values reconstructed from
      <code class="filename">pg_control</code> and values about to be changed, and then exit
      without modifying anything. This is mainly a debugging tool, but can be
      useful as a sanity check before allowing <code class="command">pg_resetwal</code>
      to proceed for real.
     </p></dd><dt><span class="term"><code class="option">-V</code><br /></span><span class="term"><code class="option">--version</code></span></dt><dd><p>Display version information, then 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, then exit.</p></dd></dl></div><p>
   The following options are only needed when
   <code class="command">pg_resetwal</code> is unable to determine appropriate values
   by reading <code class="filename">pg_control</code>.  Safe values can be determined as
   described below.  For values that take numeric arguments, hexadecimal
   values can be specified by using the prefix <code class="literal">0x</code>.
  </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-c <em class="replaceable"><code>xid</code></em>,<em class="replaceable"><code>xid</code></em></code><br /></span><span class="term"><code class="option">--commit-timestamp-ids=<em class="replaceable"><code>xid</code></em>,<em class="replaceable"><code>xid</code></em></code></span></dt><dd><p>
      Manually set the oldest and newest transaction IDs for which the commit
      time can be retrieved.
     </p><p>
      A safe value for the oldest transaction ID for which the commit time can
      be retrieved (first part) can be determined by looking
      for the numerically smallest file name in the directory
      <code class="filename">pg_commit_ts</code> under the data directory.  Conversely, a safe
      value for the newest transaction ID for which the commit time can be
      retrieved (second part) can be determined by looking for the numerically
      greatest file name in the same directory.  The file names are in
      hexadecimal.
     </p></dd><dt><span class="term"><code class="option">-e <em class="replaceable"><code>xid_epoch</code></em></code><br /></span><span class="term"><code class="option">--epoch=<em class="replaceable"><code>xid_epoch</code></em></code></span></dt><dd><p>
      Manually set the next transaction ID's epoch.
     </p><p>
      The transaction ID epoch is not actually stored anywhere in the database
      except in the field that is set by <code class="command">pg_resetwal</code>,
      so any value will work so far as the database itself is concerned.
      You might need to adjust this value to ensure that replication
      systems such as <span class="application">Slony-I</span> and
      <span class="application">Skytools</span> work correctly —
      if so, an appropriate value should be obtainable from the state of
      the downstream replicated database.
     </p></dd><dt><span class="term"><code class="option">-l <em class="replaceable"><code>walfile</code></em></code><br /></span><span class="term"><code class="option">--next-wal-file=<em class="replaceable"><code>walfile</code></em></code></span></dt><dd><p>
      Manually set the WAL starting location by specifying the name of the
      next WAL segment file.
     </p><p>
      The name of next WAL segment file should be
      larger than any WAL segment file name currently existing in
      the directory <code class="filename">pg_wal</code> under the data directory.
      These names are also in hexadecimal and have three parts.  The first
      part is the <span class="quote"><span class="quote">timeline ID</span></span> and should usually be kept the same.
      For example, if <code class="filename">00000001000000320000004A</code> is the
      largest entry in <code class="filename">pg_wal</code>, use <code class="literal">-l 00000001000000320000004B</code> or higher.
     </p><p>
      Note that when using nondefault WAL segment sizes, the numbers in the WAL
      file names are different from the LSNs that are reported by system
      functions and system views.  This option takes a WAL file name, not an
      LSN.
     </p><div class="note"><h3 class="title">Note</h3><p>
       <code class="command">pg_resetwal</code> itself looks at the files in
       <code class="filename">pg_wal</code> and chooses a default <code class="option">-l</code> setting
       beyond the last existing file name.  Therefore, manual adjustment of
       <code class="option">-l</code> should only be needed if you are aware of WAL segment
       files that are not currently present in <code class="filename">pg_wal</code>, such as
       entries in an offline archive; or if the contents of
       <code class="filename">pg_wal</code> have been lost entirely.
      </p></div></dd><dt><span class="term"><code class="option">-m <em class="replaceable"><code>mxid</code></em>,<em class="replaceable"><code>mxid</code></em></code><br /></span><span class="term"><code class="option">--multixact-ids=<em class="replaceable"><code>mxid</code></em>,<em class="replaceable"><code>mxid</code></em></code></span></dt><dd><p>
      Manually set the next and oldest multitransaction ID.
     </p><p>
      A safe value for the next multitransaction ID (first part) can be
      determined by looking for the numerically largest file name in the
      directory <code class="filename">pg_multixact/offsets</code> under the data directory,
      adding one, and then multiplying by 65536 (0x10000).  Conversely, a safe
      value for the oldest multitransaction ID (second part of
      <code class="option">-m</code>) can be determined by looking for the numerically smallest
      file name in the same directory and multiplying by 65536.  The file
      names are in hexadecimal, so the easiest way to do this is to specify
      the option value in hexadecimal and append four zeroes.
     </p></dd><dt><span class="term"><code class="option">-o <em class="replaceable"><code>oid</code></em></code><br /></span><span class="term"><code class="option">--next-oid=<em class="replaceable"><code>oid</code></em></code></span></dt><dd><p>
      Manually set the next OID.
     </p><p>
      There is no comparably easy way to determine a next OID that's beyond
      the largest one in the database, but fortunately it is not critical to
      get the next-OID setting right.
     </p></dd><dt><span class="term"><code class="option">-O <em class="replaceable"><code>mxoff</code></em></code><br /></span><span class="term"><code class="option">--multixact-offset=<em class="replaceable"><code>mxoff</code></em></code></span></dt><dd><p>
      Manually set the next multitransaction offset.
     </p><p>
      A safe value can be determined by looking for the numerically largest
      file name in the directory <code class="filename">pg_multixact/members</code> under the
      data directory, adding one, and then multiplying by 52352 (0xCC80).
      The file names are in hexadecimal.  There is no simple recipe such as
      the ones for other options of appending zeroes.
     </p></dd><dt><span class="term"><code class="option">--wal-segsize=<em class="replaceable"><code>wal_segment_size</code></em></code></span></dt><dd><p>
      Set the new WAL segment size, in megabytes.  The value must be set to a
      power of 2 between 1 and 1024 (megabytes).  See the same option of <a class="xref" href="app-initdb.html" title="initdb"><span class="refentrytitle"><span class="application">initdb</span></span></a> for more information.
     </p><div class="note"><h3 class="title">Note</h3><p>
       While <code class="command">pg_resetwal</code> will set the WAL starting address
       beyond the latest existing WAL segment file, some segment size changes
       can cause previous WAL file names to be reused.  It is recommended to
       use <code class="option">-l</code> together with this option to manually set the
       WAL starting address if WAL file name overlap will cause problems with
       your archiving strategy.
      </p></div></dd><dt><span class="term"><code class="option">-u <em class="replaceable"><code>xid</code></em></code><br /></span><span class="term"><code class="option">--oldest-transaction-id=<em class="replaceable"><code>xid</code></em></code></span></dt><dd><p>
      Manually set the oldest unfrozen transaction ID.
     </p><p>
      A safe value can be determined by looking for the numerically smallest
      file name in the directory <code class="filename">pg_xact</code> under the data directory
      and then multiplying by 1048576 (0x100000).  Note that the file names are in
      hexadecimal.  It is usually easiest to specify the option value in
      hexadecimal too. For example, if <code class="filename">0007</code> is the smallest entry
      in <code class="filename">pg_xact</code>, <code class="literal">-u 0x700000</code> will work (five
      trailing zeroes provide the proper multiplier).
     </p></dd><dt><span class="term"><code class="option">-x <em class="replaceable"><code>xid</code></em></code><br /></span><span class="term"><code class="option">--next-transaction-id=<em class="replaceable"><code>xid</code></em></code></span></dt><dd><p>
      Manually set the next transaction ID.
     </p><p>
      A safe value can be determined by looking for the numerically largest
      file name in the directory <code class="filename">pg_xact</code> under the data directory,
      adding one,
      and then multiplying by 1048576 (0x100000).  Note that the file names are in
      hexadecimal.  It is usually easiest to specify the option value in
      hexadecimal too. For example, if <code class="filename">0011</code> is the largest entry
      in <code class="filename">pg_xact</code>, <code class="literal">-x 0x1200000</code> will work (five
      trailing zeroes provide the proper multiplier).
     </p></dd></dl></div></div><div class="refsect1" id="id-1.9.5.8.7"><h2>Environment</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="envar">PG_COLOR</code></span></dt><dd><p>
      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></dd></dl></div></div><div class="refsect1" id="id-1.9.5.8.8"><h2>Notes</h2><p>
   This command must not be used when the server is
   running.  <code class="command">pg_resetwal</code> will refuse to start up if
   it finds a server lock file in the data directory.  If the
   server crashed then a lock file might have been left
   behind; in that case you can remove the lock file to allow
   <code class="command">pg_resetwal</code> to run.  But before you do
   so, make doubly certain that there is no server process still alive.
  </p><p>
   <code class="command">pg_resetwal</code> works only with servers of the same
   major version.
  </p></div><div class="refsect1" id="id-1.9.5.8.9"><h2>See Also</h2><span class="simplelist"><a class="xref" href="app-pgcontroldata.html" title="pg_controldata"><span class="refentrytitle"><span class="application">pg_controldata</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-ctl.html" title="pg_ctl">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="reference-server.html" title="PostgreSQL Server Applications">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="app-pgrewind.html" title="pg_rewind">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span class="application">pg_ctl</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> <span class="application">pg_rewind</span></td></tr></table></div></body></html>