2011-09-13 17:44:24 +00:00
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Chapter 6. Summary and Examples</title>
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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="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="prev" href="logconfig.html" title="Configuring the Logging Subsystem" />
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<link rel="next" href="txnexample_c.html" title="Transaction Example" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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2012-11-14 21:35:20 +00:00
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<p>Library Version 11.2.5.3</p>
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2011-09-13 17:44:24 +00:00
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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">Chapter 6. Summary and Examples</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="logconfig.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="txnexample_c.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="chapter" 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"><a id="wrapup"></a>Chapter 6. Summary and Examples</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<p>
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<b>Table of Contents</b>
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</p>
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<dl>
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<dt>
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<span class="sect1">
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<a href="wrapup.html#anatomy">Anatomy of a Transactional Application</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="txnexample_c.html">Transaction Example</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="inmem_txnexample_c.html">In-Memory Transaction Example</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>
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Throughout this manual we have presented the concepts and
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mechanisms that you need to provide transactional protection for
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your application. In this chapter, we summarize these
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mechanisms, and we provide a complete example of a multi-threaded
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transactional DB application.
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</p>
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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="anatomy"></a>Anatomy of a Transactional Application</h2>
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</div>
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</div>
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</div>
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<p>
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Transactional applications are characterized by performing the
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following activities:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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Create your environment handle.
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</p>
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</li>
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<li>
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<p>
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Open your environment, specifying that the following
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subsystems be used:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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Transactional Subsystem (this also initializes the
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logging subsystem).
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</p>
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</li>
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<li>
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<p>
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Memory pool (the in-memory cache).
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</p>
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</li>
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<li>
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<p>
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Logging subsystem.
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</p>
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</li>
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<li>
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<p>
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Locking subsystem (if your application is multi-process or multi-threaded).
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</p>
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</li>
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</ul>
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</div>
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<p>
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It is also highly recommended that you run normal recovery
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upon first environment open. Normal recovery examines only those logs required
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to ensure your database files are consistent relative to the information found in your
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log files.
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</p>
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</li>
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<li>
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<p>
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Optionally spawn off any utility threads that you might need. Utility
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threads can be used to run checkpoints periodically, or to
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periodically run a deadlock detector if you do not want to
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use DB's built-in deadlock detector.
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</p>
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</li>
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<li>
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<p>
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Open whatever database handles that you need.
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</p>
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</li>
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<li>
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<p>
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Spawn off worker threads. How many of these you need and
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how they split their DB workload is entirely up to your
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application's requirements. However, any worker threads
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that perform write operations will do the following:
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</p>
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<div class="orderedlist">
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<ol type="a">
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<li>
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<p>
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Begin a transaction.
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</p>
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</li>
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<li>
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<p>
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Perform one or more read and write
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operations.
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</p>
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</li>
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<li>
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<p>
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Commit the transaction if all goes well.
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</p>
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</li>
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<li>
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<p>
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Abort and retry the operation if a deadlock is
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detected.
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</p>
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</li>
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<li>
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<p>
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Abort the transaction for most other errors.
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</p>
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</li>
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</ol>
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</div>
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</li>
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<li>
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<p>
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On application shutdown:
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</p>
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<div class="orderedlist">
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<ol type="a">
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<li>
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<p>
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Make sure there are no opened cursors.
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</p>
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</li>
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<li>
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<p>
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Make sure there are no active transactions. Either
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abort or commit all transactions before shutting
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down.
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</p>
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</li>
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<li>
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<p>
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Close your databases.
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</p>
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</li>
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<li>
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<p>
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Close your environment.
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</p>
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</li>
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</ol>
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</div>
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</li>
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</ol>
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</div>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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Robust DB applications should monitor their worker threads to
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make sure they have not died unexpectedly. If a thread does
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terminate abnormally, you must shutdown all your worker threads
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and then run normal recovery (you will have to reopen your
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environment to do this). This is the only way to clear any
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resources (such as a lock or a mutex) that the abnormally
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exiting worker thread might have been holding at the time that
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it died.
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</p>
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<p>
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Failure to perform this recovery can cause your
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still-functioning worker threads to eventually block forever
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while waiting for a lock that will never be released.
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</p>
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</div>
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<p>
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In addition to these activities, which are all entirely handled by
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code within your application, there are some administrative
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activities that you should perform:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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Periodically checkpoint your application. Checkpoints will
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reduce the time to run recovery in the event that one is
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required. See <a class="xref" href="filemanagement.html#checkpoints" title="Checkpoints">Checkpoints</a>
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for details.
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</p>
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</li>
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<li>
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<p>
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Periodically back up your database and log files. This is
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required in order to fully obtain the durability guarantee
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made by DB's transaction ACID support. See
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<a class="xref" href="backuprestore.html" title="Backup Procedures">Backup Procedures</a>
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for more information.
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</p>
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</li>
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<li>
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<p>
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You may want to maintain a hot failover if 24x7 processing
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with rapid restart in the face of a disk hit is important
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to you. See <a class="xref" href="hotfailover.html" title="Using Hot Failovers">Using Hot Failovers</a>
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for more information.
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</p>
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</li>
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</ul>
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</div>
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</div>
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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="logconfig.html">Prev</a> </td>
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<td width="20%" align="center"> </td>
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<td width="40%" align="right"> <a accesskey="n" href="txnexample_c.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">Configuring the Logging Subsystem </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"> Transaction Example</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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