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<div class="sect1" lang="en" xml:lang="en">
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<div>
<h2 class="title" style="clear: both"><a id="envset_lk_detect"></a>DbEnv::set_lk_detect()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::set_lk_detect(u_int32_t detect); </pre>
<p>
Set if the deadlock detector is to be run whenever a lock conflict
occurs, and specify what lock request(s) should be rejected. As
transactions acquire locks on behalf of a single locker ID, rejecting
a lock request associated with a transaction normally requires the
transaction be aborted.
</p>
<p>
The database environment's deadlock detector configuration may also be
configured using the environment's <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file. The
syntax of the entry in that file is a single line with the string
"set_lk_detect", one or more whitespace characters, and the method
<span class="bold"><strong>detect</strong></span> parameter as a string; for
example, "set_lk_detect DB_LOCK_OLDEST". Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a>
file is read when the database environment is opened, it will
silently overrule configuration done before that time.
</p>
<p>
The <code class="methodname">DbEnv::set_lk_detect()</code> method configures a database environment,
not only operations performed using the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
handle.
</p>
<p>
The <code class="methodname">DbEnv::set_lk_detect()</code> method may be
called either before or after environment open, but once it is set
it may not be changed again during the environment's lifetime.
</p>
<p>
The <code class="methodname">DbEnv::set_lk_detect()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7920464"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp7920848"></a>detect</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>detect</strong></span> parameter configures the
deadlock detector. The deadlock detector will reject the lock request
with the lowest priority. If multiple lock requests have the lowest
priority, then the <span class="bold"><strong>detect</strong></span> parameter
is used to select which of those lock requests to reject. The
specified value must be one of the following list:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="set_lk_detect_DB_LOCK_DEFAULT"></a>
<code class="literal">DB_LOCK_DEFAULT</code>
</p>
<p>
Use whatever lock policy was specified when the database environment
was created. If no lock policy has yet been specified, set the lock
policy to DB_LOCK_RANDOM.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_EXPIRE"></a>
<code class="literal">DB_LOCK_EXPIRE</code>
</p>
<p>
Reject lock requests which have timed out. No other deadlock
detection is performed.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_MAXLOCKS"></a>
<code class="literal">DB_LOCK_MAXLOCKS</code>
</p>
<p>
Reject the lock request for the locker ID with the most locks.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_MAXWRITE"></a>
<code class="literal">DB_LOCK_MAXWRITE</code>
</p>
<p>
Reject the lock request for the locker ID with the most write locks.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_MINLOCKS"></a>
<code class="literal">DB_LOCK_MINLOCKS</code>
</p>
<p>
Reject the lock request for the locker ID with the fewest locks.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_MINWRITE"></a>
<code class="literal">DB_LOCK_MINWRITE</code>
</p>
<p>
Reject the lock request for the locker ID with the fewest write locks.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_OLDEST"></a>
<code class="literal">DB_LOCK_OLDEST</code>
</p>
<p>
Reject the lock request for the locker ID with the oldest lock.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_RANDOM"></a>
<code class="literal">DB_LOCK_RANDOM</code>
</p>
<p>
Reject the lock request for a random locker ID.
</p>
</li>
<li>
<p><a id="set_lk_detect_DB_LOCK_YOUNGEST"></a>
<code class="literal">DB_LOCK_YOUNGEST</code>
</p>
<p>
Reject the lock request for the locker ID with the youngest lock.
</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7938688"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::set_lk_detect()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp7935664"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7930088"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>,
<a class="link" href="lock.html" title="Chapter 7. The DbLock Handle">DbLock</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7936696"></a>See Also</h3>
</div>
</div>
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<a class="xref" href="lock.html#locklist" title="Locking Subsystem and Related Methods">Locking Subsystem and Related Methods</a>
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