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<title>Berkeley DB Reference Guide: Configuring locking</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Locking Subsystem</dl></h3></td>
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<h1 align=center>Configuring locking</h1>
<p>The <a href="../../api_c/env_set_lk_detect.html">DBENV->set_lk_detect</a> function specifies that the deadlock detector
should be run whenever a lock blocks. This option provides for rapid
detection of deadlocks at the expense of potentially frequent
invocations of the deadlock detector. On a fast processor with a highly
contentious application, where response time is critical, this is a good
choice. An argument to the <a href="../../api_c/env_set_lk_detect.html">DBENV->set_lk_detect</a> function indicates which
transaction to abort when a deadlock is detected. It can take on any
one of the following values:
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<p><dt><a href="../../api_c/env_set_lk_detect.html#DB_LOCK_YOUNGEST">DB_LOCK_YOUNGEST</a><dd>Abort the most recently started transaction.
<dt><a href="../../api_c/env_set_lk_detect.html#DB_LOCK_OLDEST">DB_LOCK_OLDEST</a><dd>Abort the longest lived transaction.
<dt><a href="../../api_c/env_set_lk_detect.html#DB_LOCK_RANDOM">DB_LOCK_RANDOM</a><dd>Abort whatever transaction the deadlock detector happens to find first.
<dt><a href="../../api_c/env_set_lk_detect.html#DB_LOCK_DEFAULT">DB_LOCK_DEFAULT</a><dd>Use the default policy (currently DB_RANDOM).
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<p>In general, <a href="../../api_c/env_set_lk_detect.html#DB_LOCK_DEFAULT">DB_LOCK_DEFAULT</a> is probably the correct choice. If
an application has long-running transactions, then
<a href="../../api_c/env_set_lk_detect.html#DB_LOCK_YOUNGEST">DB_LOCK_YOUNGEST</a> will guarantee that transactions eventually
complete, but it may do so at the expense of a large number of aborts.
<p>The alternative to using the <a href="../../api_c/env_set_lk_detect.html">DBENV->set_lk_detect</a> interface is
to run the deadlock detector manually, using the Berkeley DB
<a href="../../api_c/lock_detect.html">lock_detect</a> interface.
<p>The <a href="../../api_c/env_set_lk_conflicts.html">DBENV->set_lk_conflicts</a> function allows you to specify your own locking
conflicts matrix. This is an advanced configuration option, and rarely
necessary.
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