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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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 16.3 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>3 <code class="command">pg_resetwal</code> clears the write-ahead log (WAL) and4 optionally resets some other control information stored in the5 <code class="filename">pg_control</code> file. This function is sometimes needed6 if these files have become corrupted. It should be used only as a7 last resort, when the server will not start due to such corruption.8 </p><p>9 After running this command, it should be possible to start the server,10 but bear in mind that the database might contain inconsistent data due to11 partially-committed transactions. You should immediately dump your data,12 run <code class="command">initdb</code>, and restore. After restore, check for13 inconsistencies and repair as needed.14 </p><p>15 This utility can only be run by the user who installed the server, because16 it requires read/write access to the data directory.17 For safety reasons, you must specify the data directory on the command line.18 <code class="command">pg_resetwal</code> does not use the environment variable19 <code class="envar">PGDATA</code>.20 </p><p>21 If <code class="command">pg_resetwal</code> complains that it cannot determine22 valid data for <code class="filename">pg_control</code>, you can force it to proceed anyway23 by specifying the <code class="option">-f</code> (force) option. In this case plausible24 values will be substituted for the missing data. Most of the fields can be25 expected to match, but manual assistance might be needed for the next OID,26 next transaction ID and epoch, next multitransaction ID and offset, and27 WAL starting location fields. These fields can be set using the options28 discussed below. If you are not able to determine correct values for all29 these fields, <code class="option">-f</code> can still be used, but30 the recovered database must be treated with even more suspicion than31 usual: an immediate dump and restore is imperative. <span class="emphasis"><em>Do not</em></span>32 execute any data-modifying operations in the database before you dump,33 as any such action is likely to make the corruption worse.34 </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>35 Force <code class="command">pg_resetwal</code> to proceed even if it cannot determine36 valid data for <code class="filename">pg_control</code>, as explained above.37 </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>38 The <code class="option">-n</code>/<code class="option">--dry-run</code> option instructs39 <code class="command">pg_resetwal</code> to print the values reconstructed from40 <code class="filename">pg_control</code> and values about to be changed, and then exit41 without modifying anything. This is mainly a debugging tool, but can be42 useful as a sanity check before allowing <code class="command">pg_resetwal</code>43 to proceed for real.44 </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>45 The following options are only needed when46 <code class="command">pg_resetwal</code> is unable to determine appropriate values47 by reading <code class="filename">pg_control</code>. Safe values can be determined as48 described below. For values that take numeric arguments, hexadecimal49 values can be specified by using the prefix <code class="literal">0x</code>.50 </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>51 Manually set the oldest and newest transaction IDs for which the commit52 time can be retrieved.53 </p><p>54 A safe value for the oldest transaction ID for which the commit time can55 be retrieved (first part) can be determined by looking56 for the numerically smallest file name in the directory57 <code class="filename">pg_commit_ts</code> under the data directory. Conversely, a safe58 value for the newest transaction ID for which the commit time can be59 retrieved (second part) can be determined by looking for the numerically60 greatest file name in the same directory. The file names are in61 hexadecimal.62 </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>63 Manually set the next transaction ID's epoch.64 </p><p>65 The transaction ID epoch is not actually stored anywhere in the database66 except in the field that is set by <code class="command">pg_resetwal</code>,67 so any value will work so far as the database itself is concerned.68 You might need to adjust this value to ensure that replication69 systems such as <span class="application">Slony-I</span> and70 <span class="application">Skytools</span> work correctly —71 if so, an appropriate value should be obtainable from the state of72 the downstream replicated database.73 </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>74 Manually set the WAL starting location by specifying the name of the75 next WAL segment file.76 </p><p>77 The name of next WAL segment file should be78 larger than any WAL segment file name currently existing in79 the directory <code class="filename">pg_wal</code> under the data directory.80 These names are also in hexadecimal and have three parts. The first81 part is the <span class="quote">“<span class="quote">timeline ID</span>”</span> and should usually be kept the same.82 For example, if <code class="filename">00000001000000320000004A</code> is the83 largest entry in <code class="filename">pg_wal</code>, use <code class="literal">-l 00000001000000320000004B</code> or higher.84 </p><p>85 Note that when using nondefault WAL segment sizes, the numbers in the WAL86 file names are different from the LSNs that are reported by system87 functions and system views. This option takes a WAL file name, not an88 LSN.89 </p><div class="note"><h3 class="title">Note</h3><p>90 <code class="command">pg_resetwal</code> itself looks at the files in91 <code class="filename">pg_wal</code> and chooses a default <code class="option">-l</code> setting92 beyond the last existing file name. Therefore, manual adjustment of93 <code class="option">-l</code> should only be needed if you are aware of WAL segment94 files that are not currently present in <code class="filename">pg_wal</code>, such as95 entries in an offline archive; or if the contents of96 <code class="filename">pg_wal</code> have been lost entirely.97 </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>98 Manually set the next and oldest multitransaction ID.99 </p><p>100 A safe value for the next multitransaction ID (first part) can be101 determined by looking for the numerically largest file name in the102 directory <code class="filename">pg_multixact/offsets</code> under the data directory,103 adding one, and then multiplying by 65536 (0x10000). Conversely, a safe104 value for the oldest multitransaction ID (second part of105 <code class="option">-m</code>) can be determined by looking for the numerically smallest106 file name in the same directory and multiplying by 65536. The file107 names are in hexadecimal, so the easiest way to do this is to specify108 the option value in hexadecimal and append four zeroes.109 </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>110 Manually set the next OID.111 </p><p>112 There is no comparably easy way to determine a next OID that's beyond113 the largest one in the database, but fortunately it is not critical to114 get the next-OID setting right.115 </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>116 Manually set the next multitransaction offset.117 </p><p>118 A safe value can be determined by looking for the numerically largest119 file name in the directory <code class="filename">pg_multixact/members</code> under the120 data directory, adding one, and then multiplying by 52352 (0xCC80).121 The file names are in hexadecimal. There is no simple recipe such as122 the ones for other options of appending zeroes.123 </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>124 Set the new WAL segment size, in megabytes. The value must be set to a125 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.126 </p><div class="note"><h3 class="title">Note</h3><p>127 While <code class="command">pg_resetwal</code> will set the WAL starting address128 beyond the latest existing WAL segment file, some segment size changes129 can cause previous WAL file names to be reused. It is recommended to130 use <code class="option">-l</code> together with this option to manually set the131 WAL starting address if WAL file name overlap will cause problems with132 your archiving strategy.133 </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>134 Manually set the oldest unfrozen transaction ID.135 </p><p>136 A safe value can be determined by looking for the numerically smallest137 file name in the directory <code class="filename">pg_xact</code> under the data directory138 and then multiplying by 1048576 (0x100000). Note that the file names are in139 hexadecimal. It is usually easiest to specify the option value in140 hexadecimal too. For example, if <code class="filename">0007</code> is the smallest entry141 in <code class="filename">pg_xact</code>, <code class="literal">-u 0x700000</code> will work (five142 trailing zeroes provide the proper multiplier).143 </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>144 Manually set the next transaction ID.145 </p><p>146 A safe value can be determined by looking for the numerically largest147 file name in the directory <code class="filename">pg_xact</code> under the data directory,148 adding one,149 and then multiplying by 1048576 (0x100000). Note that the file names are in150 hexadecimal. It is usually easiest to specify the option value in151 hexadecimal too. For example, if <code class="filename">0011</code> is the largest entry152 in <code class="filename">pg_xact</code>, <code class="literal">-x 0x1200000</code> will work (five153 trailing zeroes provide the proper multiplier).154 </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>155 Specifies whether to use color in diagnostic messages. Possible values156 are <code class="literal">always</code>, <code class="literal">auto</code> and157 <code class="literal">never</code>.158 </p></dd></dl></div></div><div class="refsect1" id="id-1.9.5.8.8"><h2>Notes</h2><p>159 This command must not be used when the server is160 running. <code class="command">pg_resetwal</code> will refuse to start up if161 it finds a server lock file in the data directory. If the162 server crashed then a lock file might have been left163 behind; in that case you can remove the lock file to allow164 <code class="command">pg_resetwal</code> to run. But before you do165 so, make doubly certain that there is no server process still alive.166 </p><p>167 <code class="command">pg_resetwal</code> works only with servers of the same168 major version.169 </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 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> <span class="application">pg_rewind</span></td></tr></table></div></body></html>