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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>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 16.3 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 <a href="#RUNTIME-CONFIG-LOCKS" class="id_link">#</a></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> <a href="#GUC-DEADLOCK-TIMEOUT" class="id_link">#</a></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> <a href="#GUC-MAX-LOCKS-PER-TRANSACTION" class="id_link">#</a></dt><dd><p>
The shared lock table has space for
<code class="varname">max_locks_per_transaction</code> objects
(e.g., tables) per server process or prepared transaction;
hence, no more than this many distinct objects can be locked at
any one time. This parameter limits the average number of object
locks used by 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 have the
same or higher value as 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> <a href="#GUC-MAX-PRED-LOCKS-PER-TRANSACTION" class="id_link">#</a></dt><dd><p>
The shared predicate lock table has space for
<code class="varname">max_pred_locks_per_transaction</code> objects
(e.g., tables) per server process or prepared transaction;
hence, no more than this many distinct objects can be locked at
any one time. This parameter limits the average number of object
locks used by 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 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> <a href="#GUC-MAX-PRED-LOCKS-PER-RELATION" class="id_link">#</a></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> <a href="#GUC-MAX-PRED-LOCKS-PER-PAGE" class="id_link">#</a></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 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 20.13. Version and Platform Compatibility</td></tr></table></div></body></html>