1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Chapter 1. Introduction</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> 10 <link rel="up" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> 11 <link rel="prev" href="preface.html" title="Preface" /> 12 <link rel="next" href="sysfailure.html" title="A Note on System Failure" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter 1. Introduction</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="preface.html">Prev</a> </td> 22 <th width="60%" align="center"> </th> 23 <td width="20%" align="right"> <a accesskey="n" href="sysfailure.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="chapter" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title"><a id="introduction"></a>Chapter 1. Introduction</h2> 33 </div> 34 </div> 35 </div> 36 <div class="toc"> 37 <p> 38 <b>Table of Contents</b> 39 </p> 40 <dl> 41 <dt> 42 <span class="sect1"> 43 <a href="introduction.html#txnintro">Transaction Benefits</a> 44 </span> 45 </dt> 46 <dt> 47 <span class="sect1"> 48 <a href="sysfailure.html">A Note on System Failure</a> 49 </span> 50 </dt> 51 <dt> 52 <span class="sect1"> 53 <a href="apireq.html">Application Requirements</a> 54 </span> 55 </dt> 56 <dt> 57 <span class="sect1"> 58 <a href="multithread-intro.html">Multi-threaded 59 <span>and Multi-process</span> 60 Applications</a> 61 </span> 62 </dt> 63 <dt> 64 <span class="sect1"> 65 <a href="recovery-intro.html">Recoverability</a> 66 </span> 67 </dt> 68 <dt> 69 <span class="sect1"> 70 <a href="perftune-intro.html">Performance Tuning</a> 71 </span> 72 </dt> 73 </dl> 74 </div> 75 <p> 76 This book provides a thorough introduction and discussion on transactions as 77 used with Berkeley DB (DB). 78 79 80 81 It begins by offering a general overview to 82 transactions, the guarantees they provide, and the general application 83 infrastructure required to obtain full transactional protection for your 84 data. 85 </p> 86 <p> 87 This book also provides detailed examples on how to write a 88 transactional application. Both single threaded and multi-threaded <span>(as well as multi-process 89 applications)</span> are discussed. A detailed description of various 90 backup and recovery strategies is included in this manual, as is a 91 discussion on performance considerations for your transactional application. 92 </p> 93 <p> 94 You should understand the concepts from the 95 <span> 96 <em class="citetitle">Getting Started with Berkeley DB</em> 97 </span> 98 99 100 guide before reading this book. 101 </p> 102 <div class="sect1" lang="en" xml:lang="en"> 103 <div class="titlepage"> 104 <div> 105 <div> 106 <h2 class="title" style="clear: both"><a id="txnintro"></a>Transaction Benefits</h2> 107 </div> 108 </div> 109 </div> 110 <p> 111 Transactions offer your application's data protection from 112 application or system failures. That is, DB transactions offer 113 your application full ACID support: 114 </p> 115 <div class="itemizedlist"> 116 <ul type="disc"> 117 <li> 118 <p> 119 <span class="bold"><strong>A</strong></span>tomicity 120 </p> 121 <p> 122 Multiple database operations are treated as a single unit of 123 work. Once committed, all write operations performed under 124 the protection of the transaction are saved to your databases. 125 Further, in the event that you abort a transaction, all write 126 operations performed during the transaction are discarded. 127 In this event, your database is left in the state it was in 128 before the transaction began, regardless of the number or 129 type of write operations you may have performed during the 130 course of the transaction. 131 </p> 132 <p> 133 Note that DB transactions can span one or more 134 database handles. 135 </p> 136 </li> 137 <li> 138 <p> 139 <span class="bold"><strong>C</strong></span>onsistency 140 </p> 141 <p> 142 Your databases will never see a partially completed 143 transaction. This is true even if your application fails while there are 144 in-progress transactions. If the application or system fails, 145 then either all of the database changes appear when the 146 application next runs, or none of them appear. 147 </p> 148 <p> 149 In other words, whatever consistency requirements your application has will never be violated by DB. 150 If, for example, your application requires every record to include an employee ID, and your 151 code faithfully adds that ID to its database records, then DB will never 152 violate that consistency requirement. The ID will remain in the database records until such a time as your 153 application chooses to delete it. 154 </p> 155 </li> 156 <li> 157 <p> 158 <span class="bold"><strong>I</strong></span>solation 159 </p> 160 <p> 161 While a transaction is in progress, your databases will appear 162 to the transaction as if there are no other operations 163 occurring outside of the transaction. That is, operations 164 wrapped inside a transaction will always have a clean and 165 consistent view of your databases. They never have to see 166 updates currently in progress under the protection of another transaction. 167 Note, however, that isolation guarantees can be 168 169 relaxed from the default setting. See 170 <a class="xref" href="isolation.html" title="Isolation">Isolation</a> 171 for more information. 172 </p> 173 </li> 174 <li> 175 <p> 176 <span class="bold"><strong>D</strong></span>urability 177 </p> 178 <p> 179 Once committed to your databases, your modifications will 180 persist even in the event of an application or system failure. 181 Note that like isolation, your durability guarantee can be 182 relaxed. See <a class="xref" href="usingtxns.html#nodurabletxn" title="Non-Durable Transactions">Non-Durable Transactions</a> 183 for more information. 184 </p> 185 </li> 186 </ul> 187 </div> 188 </div> 189 </div> 190 <div class="navfooter"> 191 <hr /> 192 <table width="100%" summary="Navigation footer"> 193 <tr> 194 <td width="40%" align="left"><a accesskey="p" href="preface.html">Prev</a> </td> 195 <td width="20%" align="center"> </td> 196 <td width="40%" align="right"> <a accesskey="n" href="sysfailure.html">Next</a></td> 197 </tr> 198 <tr> 199 <td width="40%" align="left" valign="top">Preface </td> 200 <td width="20%" align="center"> 201 <a accesskey="h" href="index.html">Home</a> 202 </td> 203 <td width="40%" align="right" valign="top"> A Note on System Failure</td> 204 </tr> 205 </table> 206 </div> 207 </body> 208</html> 209