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106 lines
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HTML
106 lines
5.5 KiB
HTML
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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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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<html xmlns="http://www.w3.org/1999/xhtml">
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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>Environment FAQ</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="env.html" title="Chapter 9. The Berkeley DB Environment" />
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<link rel="prev" href="env_remote.html" title="Remote filesystems" />
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<link rel="next" href="cam.html" title="Chapter 10. Berkeley DB Concurrent Data Store Applications" />
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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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<p>Library Version 11.2.5.2</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">Environment FAQ</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="env_remote.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 9.
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The Berkeley DB Environment
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="cam.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="env_faq"></a>Environment FAQ</h2>
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</div>
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</div>
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</div>
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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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<span class="bold"><strong>I'm using multiple processes to access an Berkeley DB database
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environment; is there any way to ensure that two processes don't run transactional
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recovery at the same time, or that all processes have exited the database
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environment so that recovery can be run?</strong></span>
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</p>
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<p>
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See <a class="xref" href="transapp_fail.html" title="Handling failure in Transactional Data Store applications">Handling failure in Transactional Data Store applications</a> and
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<a class="xref" href="transapp_app.html" title="Architecting Transactional Data Store applications">Architecting Transactional Data Store applications</a> for a full
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discussion of this topic.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>How can I associate application information with a <a href="../api_reference/C/db.html" class="olink">DB</a> or
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<a href="../api_reference/C/env.html" class="olink">DB_ENV</a> handle?</strong></span>
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</p>
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<p>
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In the C API, the <a href="../api_reference/C/db.html" class="olink">DB</a> and <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> structures each contain an "app_private" field intended
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to be used to reference application-specific information. See the <a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a> and
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<a href="../api_reference/C/envcreate.html" class="olink">db_env_create()</a> documentation for more information.
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</p>
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<p>
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In the C++ or Java APIs, the easiest way to associate application-specific data with a
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handle is to subclass the <a href="../api_reference/CXX/db.html" class="olink">Db</a> or <a href="../api_reference/CXX/env.html" class="olink">DbEnv</a>, for example subclassing
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<a href="../api_reference/CXX/db.html" class="olink">Db</a> to get MyDb. Objects of type MyDb will still have the Berkeley DB API
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methods available on them, and you can put any extra data or methods you want into the
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MyDb class. If you are using "callback" APIs that take <a href="../api_reference/CXX/db.html" class="olink">Db</a> or
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<a href="../api_reference/CXX/env.html" class="olink">DbEnv</a> arguments (for example,
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<a href="../api_reference/CXX/dbset_bt_compare.html" class="olink">Db::set_bt_compare()</a>)
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these will always be called with the <a href="../api_reference/CXX/db.html" class="olink">Db</a> or <a href="../api_reference/CXX/env.html" class="olink">DbEnv</a> objects you
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create. So if you always use MyDb objects, you will be able to take the first argument
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to the callback function and cast it to a MyDb (in C++, cast it to (MyDb*)). That will
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allow you to access your data members or methods.
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</p>
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</li>
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</ol>
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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="env_remote.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="env.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="cam.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">Remote filesystems </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"> Chapter 10.
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Berkeley DB Concurrent Data Store Applications
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</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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