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 6. Summary and Examples</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="logconfig.html" title="Configuring the Logging Subsystem" /> 12 <link rel="next" href="txnexample_c.html" title="Transaction Example" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter 6. Summary and Examples</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="logconfig.html">Prev</a> </td> 22 <th width="60%" align="center"> </th> 23 <td width="20%" align="right"> <a accesskey="n" href="txnexample_c.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="wrapup"></a>Chapter 6. Summary and Examples</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="wrapup.html#anatomy">Anatomy of a Transactional Application</a> 44 </span> 45 </dt> 46 <dt> 47 <span class="sect1"> 48 <a href="txnexample_c.html">Transaction Example</a> 49 </span> 50 </dt> 51 <dt> 52 <span class="sect1"> 53 <a href="inmem_txnexample_c.html">In-Memory Transaction Example</a> 54 </span> 55 </dt> 56 </dl> 57 </div> 58 <p> 59 Throughout this manual we have presented the concepts and 60 mechanisms that you need to provide transactional protection for 61 your application. In this chapter, we summarize these 62 mechanisms, and we provide a complete example of a multi-threaded 63 transactional DB application. 64 </p> 65 <div class="sect1" lang="en" xml:lang="en"> 66 <div class="titlepage"> 67 <div> 68 <div> 69 <h2 class="title" style="clear: both"><a id="anatomy"></a>Anatomy of a Transactional Application</h2> 70 </div> 71 </div> 72 </div> 73 <p> 74 Transactional applications are characterized by performing the 75 following activities: 76 </p> 77 <div class="orderedlist"> 78 <ol type="1"> 79 <li> 80 <p> 81 Create your environment handle. 82 </p> 83 </li> 84 <li> 85 <p> 86 Open your environment, specifying that the following 87 subsystems be used: 88 </p> 89 <div class="itemizedlist"> 90 <ul type="disc"> 91 <li> 92 <p> 93 Transactional Subsystem (this also initializes the 94 logging subsystem). 95 </p> 96 </li> 97 <li> 98 <p> 99 Memory pool (the in-memory cache). 100 </p> 101 </li> 102 <li> 103 <p> 104 Logging subsystem. 105 </p> 106 </li> 107 <li> 108 <p> 109 Locking subsystem (if your application is multi-process or multi-threaded). 110 </p> 111 </li> 112 </ul> 113 </div> 114 <p> 115 It is also highly recommended that you run normal recovery 116 upon first environment open. Normal recovery examines only those logs required 117 to ensure your database files are consistent relative to the information found in your 118 log files. 119 </p> 120 </li> 121 <li> 122 <p> 123 Optionally spawn off any utility threads that you might need. Utility 124 threads can be used to run checkpoints periodically, or to 125 periodically run a deadlock detector if you do not want to 126 use DB's built-in deadlock detector. 127 </p> 128 </li> 129 <li> 130 <p> 131 Open whatever database handles that you need. 132 </p> 133 </li> 134 <li> 135 <p> 136 Spawn off worker threads. How many of these you need and 137 how they split their DB workload is entirely up to your 138 application's requirements. However, any worker threads 139 that perform write operations will do the following: 140 </p> 141 <div class="orderedlist"> 142 <ol type="a"> 143 <li> 144 <p> 145 Begin a transaction. 146 </p> 147 </li> 148 <li> 149 <p> 150 Perform one or more read and write 151 operations. 152 </p> 153 </li> 154 <li> 155 <p> 156 Commit the transaction if all goes well. 157 </p> 158 </li> 159 <li> 160 <p> 161 Abort and retry the operation if a deadlock is 162 detected. 163 </p> 164 </li> 165 <li> 166 <p> 167 Abort the transaction for most other errors. 168 </p> 169 </li> 170 </ol> 171 </div> 172 </li> 173 <li> 174 <p> 175 On application shutdown: 176 </p> 177 <div class="orderedlist"> 178 <ol type="a"> 179 <li> 180 <p> 181 Make sure there are no opened cursors. 182 </p> 183 </li> 184 <li> 185 <p> 186 Make sure there are no active transactions. Either 187 abort or commit all transactions before shutting 188 down. 189 </p> 190 </li> 191 <li> 192 <p> 193 Close your databases. 194 </p> 195 </li> 196 <li> 197 <p> 198 Close your environment. 199 </p> 200 </li> 201 </ol> 202 </div> 203 </li> 204 </ol> 205 </div> 206 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 207 <h3 class="title">Note</h3> 208 <p> 209 Robust DB applications should monitor their worker threads to 210 make sure they have not died unexpectedly. If a thread does 211 terminate abnormally, you must shutdown all your worker threads 212 and then run normal recovery (you will have to reopen your 213 environment to do this). This is the only way to clear any 214 resources (such as a lock or a mutex) that the abnormally 215 exiting worker thread might have been holding at the time that 216 it died. 217 </p> 218 <p> 219 Failure to perform this recovery can cause your 220 still-functioning worker threads to eventually block forever 221 while waiting for a lock that will never be released. 222 </p> 223 </div> 224 <p> 225 In addition to these activities, which are all entirely handled by 226 code within your application, there are some administrative 227 activities that you should perform: 228 </p> 229 <div class="itemizedlist"> 230 <ul type="disc"> 231 <li> 232 <p> 233 Periodically checkpoint your application. Checkpoints will 234 reduce the time to run recovery in the event that one is 235 required. See <a class="xref" href="filemanagement.html#checkpoints" title="Checkpoints">Checkpoints</a> 236 for details. 237 </p> 238 </li> 239 <li> 240 <p> 241 Periodically back up your database and log files. This is 242 required in order to fully obtain the durability guarantee 243 made by DB's transaction ACID support. See 244 <a class="xref" href="backuprestore.html" title="Backup Procedures">Backup Procedures</a> 245 for more information. 246 </p> 247 </li> 248 <li> 249 <p> 250 You may want to maintain a hot failover if 24x7 processing 251 with rapid restart in the face of a disk hit is important 252 to you. See <a class="xref" href="hotfailover.html" title="Using Hot Failovers">Using Hot Failovers</a> 253 for more information. 254 </p> 255 </li> 256 </ul> 257 </div> 258 </div> 259 </div> 260 <div class="navfooter"> 261 <hr /> 262 <table width="100%" summary="Navigation footer"> 263 <tr> 264 <td width="40%" align="left"><a accesskey="p" href="logconfig.html">Prev</a> </td> 265 <td width="20%" align="center"> </td> 266 <td width="40%" align="right"> <a accesskey="n" href="txnexample_c.html">Next</a></td> 267 </tr> 268 <tr> 269 <td width="40%" align="left" valign="top">Configuring the Logging Subsystem </td> 270 <td width="20%" align="center"> 271 <a accesskey="h" href="index.html">Home</a> 272 </td> 273 <td width="40%" align="right" valign="top"> Transaction Example</td> 274 </tr> 275 </table> 276 </div> 277 </body> 278</html> 279