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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_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><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center"><span xmlns="http://www.w3.org/1999/xhtml" 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 11.5 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></hr></div><div class="refentry" id="APP-PGRESETWAL"><div class="titlepage"></div><a id="id-1.9.5.7.1" 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-1.9.5.7.4.1"><code class="command">pg_resetwal</code> [ <code class="option">--force</code> | <code class="option">-f</code> ] [ <code class="option">--dry-run</code> | <code class="option">-n</code> ] [<em class="replaceable"><code>option</code></em>...] [ <code class="option">--pgdata</code> | <code class="option">-D</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 reload. After reload, 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 reload 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-1.9.5.7.6"><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">initdb</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">-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-1.9.5.7.7"><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-1.9.5.7.8"><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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="reference-server.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="app-pgrewind.html">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">Home</a></td><td width="40%" align="right" valign="top"> <span class="application">pg_rewind</span></td></tr></table></div></body></html>
