2011-09-13 17:44:24 +00:00
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<title>Chapter 1. Introduction</title>
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<link rel="prev" href="moreinfo.html" title="For More Information" />
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<link rel="next" href="sysfailure.html" title="A Note on System Failure" />
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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 1. Introduction</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="moreinfo.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="sysfailure.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="introduction"></a>Chapter 1. Introduction</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="introduction.html#txnintro">Transaction Benefits</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="sysfailure.html">A Note on System Failure</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="apireq.html">Application Requirements</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="multithread-intro.html">Multi-threaded
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<span>and Multi-process</span>
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Applications</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="recovery-intro.html">Recoverability</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="perftune-intro.html">Performance Tuning</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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This book provides a thorough introduction and discussion on transactions as
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used with Berkeley DB (DB).
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It begins by offering a general overview to
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transactions, the guarantees they provide, and the general application
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infrastructure required to obtain full transactional protection for your
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data.
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</p>
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<p>
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This book also provides detailed examples on how to write a
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transactional application. Both single threaded and multi-threaded <span>(as well as multi-process
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applications)</span> are discussed. A detailed description of various
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backup and recovery strategies is included in this manual, as is a
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discussion on performance considerations for your transactional application.
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</p>
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<p>
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You should understand the concepts from the
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<span>
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<em class="citetitle">Getting Started with Berkeley DB</em>
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</span>
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guide before reading this book.
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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="txnintro"></a>Transaction Benefits</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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Transactions offer your application's data protection from
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application or system failures. That is, DB transactions offer
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your application full ACID support:
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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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<span class="bold"><strong>A</strong></span>tomicity
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</p>
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<p>
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Multiple database operations are treated as a single unit of
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work. Once committed, all write operations performed under
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the protection of the transaction are saved to your databases.
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Further, in the event that you abort a transaction, all write
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operations performed during the transaction are discarded.
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In this event, your database is left in the state it was in
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before the transaction began, regardless of the number or
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type of write operations you may have performed during the
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course of the transaction.
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</p>
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<p>
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Note that DB transactions can span one or more
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database handles.
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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>C</strong></span>onsistency
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</p>
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<p>
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Your databases will never see a partially completed
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transaction. This is true even if your application fails while there are
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in-progress transactions. If the application or system fails,
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then either all of the database changes appear when the
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application next runs, or none of them appear.
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</p>
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<p>
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In other words, whatever consistency requirements your application has will never be violated by DB.
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If, for example, your application requires every record to include an employee ID, and your
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code faithfully adds that ID to its database records, then DB will never
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violate that consistency requirement. The ID will remain in the database records until such a time as your
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application chooses to delete it.
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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>I</strong></span>solation
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</p>
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<p>
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While a transaction is in progress, your databases will appear
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to the transaction as if there are no other operations
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occurring outside of the transaction. That is, operations
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wrapped inside a transaction will always have a clean and
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consistent view of your databases. They never have to see
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updates currently in progress under the protection of another transaction.
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Note, however, that isolation guarantees can be
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relaxed from the default setting. See
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<a class="xref" href="isolation.html" title="Isolation">Isolation</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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<span class="bold"><strong>D</strong></span>urability
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</p>
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<p>
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Once committed to your databases, your modifications will
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persist even in the event of an application or system failure.
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Note that like isolation, your durability guarantee can be
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relaxed. See <a class="xref" href="nodurabletxn.html" title="Non-Durable Transactions">Non-Durable Transactions</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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<td width="40%" align="left"><a accesskey="p" href="moreinfo.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="sysfailure.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">For More Information </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"> A Note on System Failure</td>
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</tr>
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</table>
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</div>
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</html>
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