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<h2 class="title" style="clear: both"><a id="lock_config"></a>Configuring locking</h2>
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<p>
The <a href="../api_reference/C/envset_lk_detect.html" class="olink">DB_ENV->set_lk_detect()</a> method specifies that the deadlock
detector should be run whenever a lock is about to block. 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 option argument to the <a href="../api_reference/C/envset_lk_detect.html" class="olink">DB_ENV->set_lk_detect()</a> method
indicates which lock requests should be rejected.
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The application can limit how long it blocks on a contested
resource. The <a href="../api_reference/C/envset_timeout.html" class="olink">DB_ENV->set_timeout()</a> method specifies the length of
the timeout. This value is checked whenever deadlock detection
is performed, so the accuracy of the timeout depends upon the
frequency of deadlock detection.
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In general, when applications are not specifying lock and
transaction timeout values, the <a href="../api_reference/C/lockdetect.html#detect_DB_LOCK_DEFAULT" class="olink">DB_LOCK_DEFAULT</a> option is
probably the correct first choice, and other options should
only be selected based on evidence that they improve
transaction throughput. If an application has long-running
transactions, <a href="../api_reference/C/lockdetect.html#detect_DB_LOCK_YOUNGEST" class="olink">DB_LOCK_YOUNGEST</a> will guarantee that
transactions eventually complete, but it may do so at the
expense of a large number of lock request rejections (and
therefore, transaction aborts).
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The alternative to using the <a href="../api_reference/C/envset_lk_detect.html" class="olink">DB_ENV->set_lk_detect()</a> method is to
explicitly perform deadlock detection using the Berkeley DB
<a href="../api_reference/C/lockdetect.html" class="olink">DB_ENV->lock_detect()</a> method.
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<p>
The <a href="../api_reference/C/envset_lk_conflicts.html" class="olink">DB_ENV->set_lk_conflicts()</a> method allows you to specify your
own locking conflicts matrix. This is an advanced
configuration option, and is almost never necessary.
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