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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>F.31. pgrowlocks</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="pgprewarm.html" title="F.30. pg_prewarm" /><link rel="next" href="pgstatstatements.html" title="F.32. pg_stat_statements" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.31. pgrowlocks</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgprewarm.html" title="F.30. pg_prewarm">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgstatstatements.html" title="F.32. pg_stat_statements">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGROWLOCKS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.31. pgrowlocks</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgrowlocks.html#id-1.11.7.40.5">F.31.1. Overview</a></span></dt><dt><span class="sect2"><a href="pgrowlocks.html#id-1.11.7.40.6">F.31.2. Sample Output</a></span></dt><dt><span class="sect2"><a href="pgrowlocks.html#id-1.11.7.40.7">F.31.3. Author</a></span></dt></dl></div><a id="id-1.11.7.40.2" class="indexterm"></a><p>
The <code class="filename">pgrowlocks</code> module provides a function to show row
locking information for a specified table.
</p><p>
By default use is restricted to superusers, roles with privileges of the
<code class="literal">pg_stat_scan_tables</code> role, and users with
<code class="literal">SELECT</code> permissions on the table.
</p><div class="sect2" id="id-1.11.7.40.5"><div class="titlepage"><div><div><h3 class="title">F.31.1. Overview</h3></div></div></div><a id="id-1.11.7.40.5.2" class="indexterm"></a><pre class="synopsis">
pgrowlocks(text) returns setof record
</pre><p>
The parameter is the name of a table. The result is a set of records,
with one row for each locked row within the table. The output columns
are shown in <a class="xref" href="pgrowlocks.html#PGROWLOCKS-COLUMNS" title="Table F.19. pgrowlocks Output Columns">Table F.19</a>.
</p><div class="table" id="PGROWLOCKS-COLUMNS"><p class="title"><strong>Table F.19. <code class="function">pgrowlocks</code> Output Columns</strong></p><div class="table-contents"><table class="table" summary="pgrowlocks Output Columns" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">locked_row</code></td><td><code class="type">tid</code></td><td>Tuple ID (TID) of locked row</td></tr><tr><td><code class="structfield">locker</code></td><td><code class="type">xid</code></td><td>Transaction ID of locker, or multixact ID if multitransaction</td></tr><tr><td><code class="structfield">multi</code></td><td><code class="type">boolean</code></td><td>True if locker is a multitransaction</td></tr><tr><td><code class="structfield">xids</code></td><td><code class="type">xid[]</code></td><td>Transaction IDs of lockers (more than one if multitransaction)</td></tr><tr><td><code class="structfield">modes</code></td><td><code class="type">text[]</code></td><td>Lock mode of lockers (more than one if multitransaction),
an array of <code class="literal">Key Share</code>, <code class="literal">Share</code>,
<code class="literal">For No Key Update</code>, <code class="literal">No Key Update</code>,
<code class="literal">For Update</code>, <code class="literal">Update</code>.</td></tr><tr><td><code class="structfield">pids</code></td><td><code class="type">integer[]</code></td><td>Process IDs of locking backends (more than one if multitransaction)</td></tr></tbody></table></div></div><br class="table-break" /><p>
<code class="function">pgrowlocks</code> takes <code class="literal">AccessShareLock</code> for the
target table and reads each row one by one to collect the row locking
information. This is not very speedy for a large table. Note that:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
If an <code class="literal">ACCESS EXCLUSIVE</code> lock is taken on the table,
<code class="function">pgrowlocks</code> will be blocked.
</p></li><li class="listitem"><p>
<code class="function">pgrowlocks</code> is not guaranteed to produce a
self-consistent snapshot. It is possible that a new row lock is taken,
or an old lock is freed, during its execution.
</p></li></ol></div><p>
<code class="function">pgrowlocks</code> does not show the contents of locked
rows. If you want to take a look at the row contents at the same time, you
could do something like this:
</p><pre class="programlisting">
SELECT * FROM accounts AS a, pgrowlocks('accounts') AS p
WHERE p.locked_row = a.ctid;
</pre><p>
Be aware however that such a query will be very inefficient.
</p></div><div class="sect2" id="id-1.11.7.40.6"><div class="titlepage"><div><div><h3 class="title">F.31.2. Sample Output</h3></div></div></div><pre class="screen">
=# SELECT * FROM pgrowlocks('t1');
locked_row | locker | multi | xids | modes | pids
------------+--------+-------+-------+----------------+--------
(0,1) | 609 | f | {609} | {"For Share"} | {3161}
(0,2) | 609 | f | {609} | {"For Share"} | {3161}
(0,3) | 607 | f | {607} | {"For Update"} | {3107}
(0,4) | 607 | f | {607} | {"For Update"} | {3107}
(4 rows)
</pre></div><div class="sect2" id="id-1.11.7.40.7"><div class="titlepage"><div><div><h3 class="title">F.31.3. Author</h3></div></div></div><p>
Tatsuo Ishii
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pgprewarm.html" title="F.30. pg_prewarm">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pgstatstatements.html" title="F.32. pg_stat_statements">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.30. pg_prewarm </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.32. pg_stat_statements</td></tr></table></div></body></html>
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