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192 lines
8.1 KiB
HTML
192 lines
8.1 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>Application Requirements</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="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="introduction.html" title="Chapter 1. Introduction" />
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<link rel="prev" href="sysfailure.html" title="A Note on System Failure" />
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<link rel="next" href="multithread-intro.html" title="Multi-threaded and Multi-process 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">Application Requirements</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="sysfailure.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 1. Introduction</th>
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<td width="20%" align="right"> <a accesskey="n" href="multithread-intro.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="apireq"></a>Application Requirements</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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In order to use transactions, your application has certain
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requirements beyond what is required of non-transactional protected
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applications. They are:
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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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Environments.
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</p>
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<p>
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Environments are optional for non-transactional
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applications, but they are required for transactional
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applications.
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</p>
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<p>
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Environment usage is described in detail in
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<a class="xref" href="usingtxns.html" title="Chapter 3. Transaction Basics">Transaction Basics</a>.
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</p>
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</li>
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<li>
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<p>
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Transaction subsystem.
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</p>
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<p>
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In order to use transactions, you must explicitly
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enable the transactional subsystem for your
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application, and this must be done at the time that
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your environment is first created.
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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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<p>
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The logging subsystem is required for recovery purposes, but
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its usage also means your application may require a
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little more administrative effort than it does when logging
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is not in use. See <a class="xref" href="filemanagement.html" title="Chapter 5. Managing DB Files">Managing DB Files</a> 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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<span>DbTxn</span>
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handles.
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</p>
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<p>
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In order to obtain the atomicity guarantee offered by
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the transactional subsystem (that is, combine multiple
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operations in a single unit of work), your application must use
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transaction handles. These handles are obtained from your
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<span>DbEnv</span>
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objects. They should normally be short-lived, and their usage is
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reasonably simple. To complete a transaction and save
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the work it performed, you
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call its <code class="methodname">commit()</code> method. To
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complete a transaction and discard its work, you call its
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<code class="methodname">abort()</code> method.
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</p>
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<p>
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In addition, it is possible to use auto commit if you want
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to transactional protect a single write operation. Auto
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commit allows a transaction to be used without
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obtaining an explicit transaction handle. See
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<a class="xref" href="autocommit.html" title="Auto Commit">Auto Commit</a>
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for information on how to use auto commit.
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</p>
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</li>
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<li>
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<p>
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Database open requirements.
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</p>
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<p>
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<span>In addition to using
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environments and initializing the
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correct subsystems, your</span>
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application must transaction protect the database
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opens<span>,
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and any secondary index associations,</span>
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if subsequent operations on the databases are to be transaction
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protected. The database open and secondary index
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association are commonly transaction protected using
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auto commit.
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</p>
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</li>
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<li>
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<p>
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Deadlock detection.
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</p>
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<p>
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Typically transactional applications use multiple
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threads of control when accessing the database.
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Any time multiple threads are used on a single resource,
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the potential for lock contention arises. In turn, lock
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contention can lead to deadlocks. See
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<a class="xref" href="blocking_deadlocks.html" title="Locks, Blocks, and Deadlocks">Locks, Blocks, and Deadlocks</a>
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for more information.
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</p>
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<p>
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Therefore, transactional applications must frequently
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include code for detecting and responding to deadlocks.
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Note that this requirement is not
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<span class="emphasis"><em>specific</em></span> to transactions
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– you can certainly write concurrent
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non-transactional DB applications. Further, not
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every transactional application uses concurrency and
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so not every transactional application must
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manage deadlocks. Still, deadlock management is so
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frequently a characteristic of transactional
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applications that we discuss it in this
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book. See <a class="xref" href="txnconcurrency.html" title="Chapter 4. Concurrency">Concurrency</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 class="navfooter">
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<hr />
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|
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<table width="100%" summary="Navigation footer">
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|||
|
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<tr>
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|||
|
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<td width="40%" align="left"><a accesskey="p" href="sysfailure.html">Prev</a> </td>
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|||
|
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<td width="20%" align="center">
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<a accesskey="u" href="introduction.html">Up</a>
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|||
|
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</td>
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|||
|
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<td width="40%" align="right"> <a accesskey="n" href="multithread-intro.html">Next</a></td>
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|||
|
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</tr>
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|||
|
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<tr>
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|||
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<td width="40%" align="left" valign="top">A Note on System Failure </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"> Multi-threaded
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<span>and Multi-process</span>
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Applications</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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