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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>20.12. Lock Management</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="runtime-config-client.html" title="20.11. Client Connection Defaults" /><link rel="next" href="runtime-config-compatible.html" title="20.13. Version and Platform Compatibility" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">20.12. Lock Management</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="runtime-config-client.html" title="20.11. Client Connection Defaults">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="runtime-config.html" title="Chapter 20. Server Configuration">Up</a></td><th width="60%" align="center">Chapter 20. Server Configuration</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="runtime-config-compatible.html" title="20.13. Version and Platform Compatibility">Next</a></td></tr></table><hr /></div><div class="sect1" id="RUNTIME-CONFIG-LOCKS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">20.12. Lock Management</h2></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="GUC-DEADLOCK-TIMEOUT"><span class="term"><code class="varname">deadlock_timeout</code> (<code class="type">integer</code>)
      <a id="id-1.6.7.15.2.1.1.3" class="indexterm"></a>
      <a id="id-1.6.7.15.2.1.1.4" class="indexterm"></a>
      <a id="id-1.6.7.15.2.1.1.5" class="indexterm"></a>
      </span></dt><dd><p>
        This is the amount of time to wait on a lock
        before checking to see if there is a deadlock condition. The
        check for deadlock is relatively expensive, so the server doesn't run
        it every time it waits for a lock. We optimistically assume
        that deadlocks are not common in production applications and
        just wait on the lock for a while before checking for a
        deadlock. Increasing this value reduces the amount of time
        wasted in needless deadlock checks, but slows down reporting of
        real deadlock errors.
        If this value is specified without units, it is taken as milliseconds.
        The default is one second (<code class="literal">1s</code>),
        which is probably about the smallest value you would want in
        practice. On a heavily loaded server you might want to raise it.
        Ideally the setting should exceed your typical transaction time,
        so as to improve the odds that a lock will be released before
        the waiter decides to check for deadlock.
        Only superusers and users with the appropriate <code class="literal">SET</code>
        privilege can change this setting.
       </p><p>
        When <a class="xref" href="runtime-config-logging.html#GUC-LOG-LOCK-WAITS">log_lock_waits</a> is set,
        this parameter also determines the amount of time to wait before
        a log message is issued about the lock wait.  If you are trying
        to investigate locking delays you might want to set a shorter than
        normal <code class="varname">deadlock_timeout</code>.
       </p></dd><dt id="GUC-MAX-LOCKS-PER-TRANSACTION"><span class="term"><code class="varname">max_locks_per_transaction</code> (<code class="type">integer</code>)
      <a id="id-1.6.7.15.2.2.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        The shared lock table tracks locks on
        <code class="varname">max_locks_per_transaction</code> * (<a class="xref" href="runtime-config-connection.html#GUC-MAX-CONNECTIONS">max_connections</a> + <a class="xref" href="runtime-config-resource.html#GUC-MAX-PREPARED-TRANSACTIONS">max_prepared_transactions</a>) objects (e.g.,  tables);
        hence, no more than this many distinct objects can be locked at
        any one time.  This parameter controls the average number of object
        locks allocated for each transaction;  individual transactions
        can lock more objects as long as the locks of all transactions
        fit in the lock table.  This is <span class="emphasis"><em>not</em></span> the number of
        rows that can be locked; that value is unlimited.  The default,
        64, has historically proven sufficient, but you might need to
        raise this value if you have queries that touch many different
        tables in a single transaction, e.g., query of a parent table with
        many children.  This parameter can only be set at server start.
       </p><p>
        When running a standby server, you must set this parameter to the
        same or higher value than on the primary server. Otherwise, queries
        will not be allowed in the standby server.
       </p></dd><dt id="GUC-MAX-PRED-LOCKS-PER-TRANSACTION"><span class="term"><code class="varname">max_pred_locks_per_transaction</code> (<code class="type">integer</code>)
      <a id="id-1.6.7.15.2.3.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        The shared predicate lock table tracks locks on
        <code class="varname">max_pred_locks_per_transaction</code> * (<a class="xref" href="runtime-config-connection.html#GUC-MAX-CONNECTIONS">max_connections</a> + <a class="xref" href="runtime-config-resource.html#GUC-MAX-PREPARED-TRANSACTIONS">max_prepared_transactions</a>) objects (e.g., tables);
        hence, no more than this many distinct objects can be locked at
        any one time.  This parameter controls the average number of object
        locks allocated for each transaction;  individual transactions
        can lock more objects as long as the locks of all transactions
        fit in the lock table.  This is <span class="emphasis"><em>not</em></span> the number of
        rows that can be locked; that value is unlimited.  The default,
        64, has generally been sufficient in testing, but you might need to
        raise this value if you have clients that touch many different
        tables in a single serializable transaction. This parameter can
        only be set at server start.
       </p></dd><dt id="GUC-MAX-PRED-LOCKS-PER-RELATION"><span class="term"><code class="varname">max_pred_locks_per_relation</code> (<code class="type">integer</code>)
      <a id="id-1.6.7.15.2.4.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        This controls how many pages or tuples of a single relation can be
        predicate-locked before the lock is promoted to covering the whole
        relation.  Values greater than or equal to zero mean an absolute
        limit, while negative values
        mean <a class="xref" href="runtime-config-locks.html#GUC-MAX-PRED-LOCKS-PER-TRANSACTION">max_pred_locks_per_transaction</a> divided by
        the absolute value of this setting.  The default is -2, which keeps
        the behavior from previous versions of <span class="productname">PostgreSQL</span>.
        This parameter can only be set in the <code class="filename">postgresql.conf</code>
        file or on the server command line.
       </p></dd><dt id="GUC-MAX-PRED-LOCKS-PER-PAGE"><span class="term"><code class="varname">max_pred_locks_per_page</code> (<code class="type">integer</code>)
      <a id="id-1.6.7.15.2.5.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        This controls how many rows on a single page can be predicate-locked
        before the lock is promoted to covering the whole page.  The default
        is 2.  This parameter can only be set in
        the <code class="filename">postgresql.conf</code> file or on the server command line.
       </p></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="runtime-config-client.html" title="20.11. Client Connection Defaults">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="runtime-config.html" title="Chapter 20. Server Configuration">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="runtime-config-compatible.html" title="20.13. Version and Platform Compatibility">Next</a></td></tr><tr><td width="40%" align="left" valign="top">20.11. Client Connection Defaults </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"> 20.13. Version and Platform Compatibility</td></tr></table></div></body></html>