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90 lines
4.7 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Configuring locking</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="lock.html" title="Chapter 16. The Locking Subsystem" />
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<link rel="prev" href="lock.html" title="Chapter 16. The Locking Subsystem" />
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<link rel="next" href="lock_max.html" title="Configuring locking: sizing the system" />
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<p>Library Version 11.2.5.3</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Configuring locking</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="lock.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 16.
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The Locking Subsystem
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="lock_max.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="lock_config"></a>Configuring locking</h2>
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</div>
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</div>
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</div>
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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
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should be run whenever a lock is about to block. This option provides
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for rapid detection of deadlocks at the expense of potentially frequent
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invocations of the deadlock detector. On a fast processor with a highly
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contentious application where response time is critical, this is a good
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choice. An option argument to the <a href="../api_reference/C/envset_lk_detect.html" class="olink">DB_ENV->set_lk_detect()</a> method
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indicates which lock requests should be rejected.</p>
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<p>The application can limit how long it blocks on a contested resource.
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The <a href="../api_reference/C/envset_timeout.html" class="olink">DB_ENV->set_timeout()</a> method specifies the length of the timeout.
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This value is checked whenever deadlock detection is performed,
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so the accuracy of the timeout depends upon the frequency of
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deadlock detection.</p>
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<p>In general, when applications are not specifying lock and transaction
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timeout values, the <a href="../api_reference/C/lockdetect.html#detect_DB_LOCK_DEFAULT" class="olink">DB_LOCK_DEFAULT</a> option is probably the
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correct first choice, and other options should only be selected based
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on evidence that they improve transaction throughput. If an application
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has long-running transactions, <a href="../api_reference/C/lockdetect.html#detect_DB_LOCK_YOUNGEST" class="olink">DB_LOCK_YOUNGEST</a> will guarantee
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that transactions eventually complete, but it may do so at the expense
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of a large number of lock request rejections (and therefore, transaction
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aborts).</p>
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<p>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
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explicitly perform deadlock detection using the Berkeley DB
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<a href="../api_reference/C/lockdetect.html" class="olink">DB_ENV->lock_detect()</a> method.</p>
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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
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locking conflicts matrix. This is an advanced configuration option,
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and is almost never necessary.</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="lock.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="lock.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="lock_max.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Chapter 16.
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The Locking Subsystem
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</td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Configuring locking: sizing the system</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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